Muehlenhoff has submitted this change and it was merged.
Change subject: Add backports of recent Linux kernel NMI security fixes
......................................................................
Add backports of recent Linux kernel NMI security fixes
Change-Id: I1f42ee028cfccbe857626af4f892c97261d1b32f
---
M debian/changelog
A
debian/patches/bugfix/x86/0001-x86-asm-entry-64-Fold-the-test_in_nmi-macro-into-its.patch
A debian/patches/bugfix/x86/0002-x86-asm-entry-64-Remove-a-redundant-jump.patch
A
debian/patches/bugfix/x86/0004-x86-nmi-Enable-nested-do_nmi-handling-for-64-bit-ker.patch
A debian/patches/bugfix/x86/0005-x86-nmi-64-Remove-asm-code-that-saves-cr2.patch
A
debian/patches/bugfix/x86/0006-x86-nmi-64-Switch-stacks-on-userspace-NMI-entry.patch
A debian/patches/bugfix/x86/0007-x86-nmi-64-Improve-nested-NMI-comments.patch
A debian/patches/bugfix/x86/0008-x86-nmi-64-Reorder-nested-NMI-checks.patch
A
debian/patches/bugfix/x86/0009-x86-nmi-64-Use-DF-to-avoid-userspace-RSP-confusing-n.patch
M debian/patches/series
10 files changed, 946 insertions(+), 0 deletions(-)
Approvals:
Muehlenhoff: Verified; Looks good to me, approved
diff --git a/debian/changelog b/debian/changelog
index 5db451d..8b2c111 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -7,6 +7,8 @@
-> CVE-2015-4692 (ce40cd3fc7fa40a6119e5fe6c0f2bc0eb4541009)
http://kernel.ubuntu.com/stable/ChangeLog-3.19.8-ckt4
-> CVE-2015-3212 (2d45a02d0166caf2627fe91897c6ffc3b19514c4)
+ * Add backport of NMI security patches:
+ Fixes CVE-2015-3290, CVE-2015-3291, CVE-2015-5157
-- Moritz Muehlenhoff <[email protected]> Mon, 20 Jul 2015 10:07:54
+0200
diff --git
a/debian/patches/bugfix/x86/0001-x86-asm-entry-64-Fold-the-test_in_nmi-macro-into-its.patch
b/debian/patches/bugfix/x86/0001-x86-asm-entry-64-Fold-the-test_in_nmi-macro-into-its.patch
new file mode 100644
index 0000000..635bdc6
--- /dev/null
+++
b/debian/patches/bugfix/x86/0001-x86-asm-entry-64-Fold-the-test_in_nmi-macro-into-its.patch
@@ -0,0 +1,71 @@
+From: Denys Vlasenko <[email protected]>
+Date: Wed, 1 Apr 2015 16:50:57 +0200
+Subject: [PATCH 1/9] x86/asm/entry/64: Fold the 'test_in_nmi' macro into its
+ only user
+Origin: https://git.kernel.org/linus/0784b36448a2a85b95b6eb21a69b9045c896c065
+
+No code changes.
+
+Signed-off-by: Denys Vlasenko <[email protected]>
+Acked-by: Borislav Petkov <[email protected]>
+Cc: Alexei Starovoitov <[email protected]>
+Cc: Andy Lutomirski <[email protected]>
+Cc: Borislav Petkov <[email protected]>
+Cc: Frederic Weisbecker <[email protected]>
+Cc: H. Peter Anvin <[email protected]>
+Cc: Kees Cook <[email protected]>
+Cc: Linus Torvalds <[email protected]>
+Cc: Oleg Nesterov <[email protected]>
+Cc: Steven Rostedt <[email protected]>
+Cc: Will Drewry <[email protected]>
+Link:
http://lkml.kernel.org/r/[email protected]
+Signed-off-by: Ingo Molnar <[email protected]>
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 28 +++++++++++++---------------
+ 1 file changed, 13 insertions(+), 15 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1441,19 +1441,7 @@ ENTRY(error_exit)
+ CFI_ENDPROC
+ END(error_exit)
+
+-/*
+- * Test if a given stack is an NMI stack or not.
+- */
+- .macro test_in_nmi reg stack nmi_ret normal_ret
+- cmpq %\reg, \stack
+- ja \normal_ret
+- subq $EXCEPTION_STKSZ, %\reg
+- cmpq %\reg, \stack
+- jb \normal_ret
+- jmp \nmi_ret
+- .endm
+-
+- /* runs on exception stack */
++/* Runs on exception stack */
+ ENTRY(nmi)
+ INTR_FRAME
+ PARAVIRT_ADJUST_EXCEPTION_FRAME
+@@ -1514,8 +1502,18 @@ ENTRY(nmi)
+ * We check the variable because the first NMI could be in a
+ * breakpoint routine using a breakpoint stack.
+ */
+- lea 6*8(%rsp), %rdx
+- test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
++ lea 6*8(%rsp), %rdx
++ /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp))
*/
++ cmpq %rdx, 4*8(%rsp)
++ /* If the stack pointer is above the NMI stack, this is a normal NMI */
++ ja first_nmi
++ subq $EXCEPTION_STKSZ, %rdx
++ cmpq %rdx, 4*8(%rsp)
++ /* If it is below the NMI stack, it is a normal NMI */
++ jb first_nmi
++ /* Ah, it is within the NMI stack, treat it as nested */
++ jmp nested_nmi
++
+ CFI_REMEMBER_STATE
+
+ nested_nmi:
diff --git
a/debian/patches/bugfix/x86/0002-x86-asm-entry-64-Remove-a-redundant-jump.patch
b/debian/patches/bugfix/x86/0002-x86-asm-entry-64-Remove-a-redundant-jump.patch
new file mode 100644
index 0000000..31cf68f
--- /dev/null
+++
b/debian/patches/bugfix/x86/0002-x86-asm-entry-64-Remove-a-redundant-jump.patch
@@ -0,0 +1,42 @@
+From: Denys Vlasenko <[email protected]>
+Date: Tue, 7 Apr 2015 22:43:41 +0200
+Subject: [PATCH 2/9] x86/asm/entry/64: Remove a redundant jump
+Origin: https://git.kernel.org/linus/a30b0085f54efae11f6256df4e4a16af7eefc1c4
+
+Jumping to the very next instruction is not very useful:
+
+ jmp label
+ label:
+
+Removing the jump.
+
+Signed-off-by: Denys Vlasenko <[email protected]>
+Cc: Alexei Starovoitov <[email protected]>
+Cc: Andy Lutomirski <[email protected]>
+Cc: Borislav Petkov <[email protected]>
+Cc: Brian Gerst <[email protected]>
+Cc: Frederic Weisbecker <[email protected]>
+Cc: H. Peter Anvin <[email protected]>
+Cc: Kees Cook <[email protected]>
+Cc: Linus Torvalds <[email protected]>
+Cc: Oleg Nesterov <[email protected]>
+Cc: Steven Rostedt <[email protected]>
+Cc: Thomas Gleixner <[email protected]>
+Cc: Will Drewry <[email protected]>
+Link:
http://lkml.kernel.org/r/[email protected]
+Signed-off-by: Ingo Molnar <[email protected]>
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 1 -
+ 1 file changed, 1 deletion(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1512,7 +1512,6 @@ ENTRY(nmi)
+ /* If it is below the NMI stack, it is a normal NMI */
+ jb first_nmi
+ /* Ah, it is within the NMI stack, treat it as nested */
+- jmp nested_nmi
+
+ CFI_REMEMBER_STATE
+
diff --git
a/debian/patches/bugfix/x86/0004-x86-nmi-Enable-nested-do_nmi-handling-for-64-bit-ker.patch
b/debian/patches/bugfix/x86/0004-x86-nmi-Enable-nested-do_nmi-handling-for-64-bit-ker.patch
new file mode 100644
index 0000000..2804ad9
--- /dev/null
+++
b/debian/patches/bugfix/x86/0004-x86-nmi-Enable-nested-do_nmi-handling-for-64-bit-ker.patch
@@ -0,0 +1,189 @@
+From: Andy Lutomirski <[email protected]>
+Date: Fri, 10 Jul 2015 11:19:37 -0700
+Subject: [PATCH 4/9] x86/nmi: Enable nested do_nmi handling for 64-bit kernels
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=aad62c1521e5904e376b88e71c60849954cbf9de
+
+32-bit kernels handle nested NMIs in C. Enable the exact same
+handling on 64-bit kernels as well. This isn't currently necessary,
+but it will become necessary once the asm code starts allowing
+limited nesting.
+
+This is a prerequisite for the fix for CVE-2015-3290.
+
+Cc: [email protected]
+Reviewed-by: Steven Rostedt <[email protected]>
+Signed-off-by: Andy Lutomirski <[email protected]>
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/nmi.c | 123 +++++++++++++++++++++-----------------------------
+ 1 file changed, 52 insertions(+), 71 deletions(-)
+
+--- a/arch/x86/kernel/nmi.c
++++ b/arch/x86/kernel/nmi.c
+@@ -408,15 +408,15 @@ static void default_do_nmi(struct pt_reg
+ NOKPROBE_SYMBOL(default_do_nmi);
+
+ /*
+- * NMIs can hit breakpoints which will cause it to lose its
+- * NMI context with the CPU when the breakpoint does an iret.
+- */
+-#ifdef CONFIG_X86_32
+-/*
+- * For i386, NMIs use the same stack as the kernel, and we can
+- * add a workaround to the iret problem in C (preventing nested
+- * NMIs if an NMI takes a trap). Simply have 3 states the NMI
+- * can be in:
++ * NMIs can hit breakpoints which will cause it to lose its NMI context
++ * with the CPU when the breakpoint or page fault does an IRET.
++ *
++ * As a result, NMIs can nest if NMIs get unmasked due an IRET during
++ * NMI processing. On x86_64, the asm glue protects us from nested NMIs
++ * if the outer NMI came from kernel mode, but we can still nest if the
++ * outer NMI came from user mode.
++ *
++ * To handle these nested NMIs, we have three states:
+ *
+ * 1) not running
+ * 2) executing
+@@ -430,15 +430,14 @@ NOKPROBE_SYMBOL(default_do_nmi);
+ * (Note, the latch is binary, thus multiple NMIs triggering,
+ * when one is running, are ignored. Only one NMI is restarted.)
+ *
+- * If an NMI hits a breakpoint that executes an iret, another
+- * NMI can preempt it. We do not want to allow this new NMI
+- * to run, but we want to execute it when the first one finishes.
+- * We set the state to "latched", and the exit of the first NMI will
+- * perform a dec_return, if the result is zero (NOT_RUNNING), then
+- * it will simply exit the NMI handler. If not, the dec_return
+- * would have set the state to NMI_EXECUTING (what we want it to
+- * be when we are running). In this case, we simply jump back
+- * to rerun the NMI handler again, and restart the 'latched' NMI.
++ * If an NMI executes an iret, another NMI can preempt it. We do not
++ * want to allow this new NMI to run, but we want to execute it when the
++ * first one finishes. We set the state to "latched", and the exit of
++ * the first NMI will perform a dec_return, if the result is zero
++ * (NOT_RUNNING), then it will simply exit the NMI handler. If not, the
++ * dec_return would have set the state to NMI_EXECUTING (what we want it
++ * to be when we are running). In this case, we simply jump back to
++ * rerun the NMI handler again, and restart the 'latched' NMI.
+ *
+ * No trap (breakpoint or page fault) should be hit before nmi_restart,
+ * thus there is no race between the first check of state for NOT_RUNNING
+@@ -461,49 +460,36 @@ enum nmi_states {
+ static DEFINE_PER_CPU(enum nmi_states, nmi_state);
+ static DEFINE_PER_CPU(unsigned long, nmi_cr2);
+
+-#define nmi_nesting_preprocess(regs) \
+- do { \
+- if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \
+- this_cpu_write(nmi_state, NMI_LATCHED); \
+- return; \
+- } \
+- this_cpu_write(nmi_state, NMI_EXECUTING); \
+- this_cpu_write(nmi_cr2, read_cr2()); \
+- } while (0); \
+- nmi_restart:
+-
+-#define nmi_nesting_postprocess() \
+- do { \
+- if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \
+- write_cr2(this_cpu_read(nmi_cr2)); \
+- if (this_cpu_dec_return(nmi_state)) \
+- goto nmi_restart; \
+- } while (0)
+-#else /* x86_64 */
++#ifdef CONFIG_X86_64
+ /*
+- * In x86_64 things are a bit more difficult. This has the same problem
+- * where an NMI hitting a breakpoint that calls iret will remove the
+- * NMI context, allowing a nested NMI to enter. What makes this more
+- * difficult is that both NMIs and breakpoints have their own stack.
+- * When a new NMI or breakpoint is executed, the stack is set to a fixed
+- * point. If an NMI is nested, it will have its stack set at that same
+- * fixed address that the first NMI had, and will start corrupting the
+- * stack. This is handled in entry_64.S, but the same problem exists with
+- * the breakpoint stack.
+- *
+- * If a breakpoint is being processed, and the debug stack is being used,
+- * if an NMI comes in and also hits a breakpoint, the stack pointer
+- * will be set to the same fixed address as the breakpoint that was
+- * interrupted, causing that stack to be corrupted. To handle this case,
+- * check if the stack that was interrupted is the debug stack, and if
+- * so, change the IDT so that new breakpoints will use the current stack
+- * and not switch to the fixed address. On return of the NMI, switch back
+- * to the original IDT.
++ * In x86_64, we need to handle breakpoint -> NMI -> breakpoint. Without
++ * some care, the inner breakpoint will clobber the outer breakpoint's
++ * stack.
++ *
++ * If a breakpoint is being processed, and the debug stack is being
++ * used, if an NMI comes in and also hits a breakpoint, the stack
++ * pointer will be set to the same fixed address as the breakpoint that
++ * was interrupted, causing that stack to be corrupted. To handle this
++ * case, check if the stack that was interrupted is the debug stack, and
++ * if so, change the IDT so that new breakpoints will use the current
++ * stack and not switch to the fixed address. On return of the NMI,
++ * switch back to the original IDT.
+ */
+ static DEFINE_PER_CPU(int, update_debug_stack);
++#endif
+
+-static inline void nmi_nesting_preprocess(struct pt_regs *regs)
++dotraplinkage notrace void
++do_nmi(struct pt_regs *regs, long error_code)
+ {
++ if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
++ this_cpu_write(nmi_state, NMI_LATCHED);
++ return;
++ }
++ this_cpu_write(nmi_state, NMI_EXECUTING);
++ this_cpu_write(nmi_cr2, read_cr2());
++nmi_restart:
++
++#ifdef CONFIG_X86_64
+ /*
+ * If we interrupted a breakpoint, it is possible that
+ * the nmi handler will have breakpoints too. We need to
+@@ -514,22 +500,8 @@ static inline void nmi_nesting_preproces
+ debug_stack_set_zero();
+ this_cpu_write(update_debug_stack, 1);
+ }
+-}
+-
+-static inline void nmi_nesting_postprocess(void)
+-{
+- if (unlikely(this_cpu_read(update_debug_stack))) {
+- debug_stack_reset();
+- this_cpu_write(update_debug_stack, 0);
+- }
+-}
+ #endif
+
+-dotraplinkage notrace void
+-do_nmi(struct pt_regs *regs, long error_code)
+-{
+- nmi_nesting_preprocess(regs);
+-
+ nmi_enter();
+
+ inc_irq_stat(__nmi_count);
+@@ -539,8 +511,17 @@ do_nmi(struct pt_regs *regs, long error_
+
+ nmi_exit();
+
+- /* On i386, may loop back to preprocess */
+- nmi_nesting_postprocess();
++#ifdef CONFIG_X86_64
++ if (unlikely(this_cpu_read(update_debug_stack))) {
++ debug_stack_reset();
++ this_cpu_write(update_debug_stack, 0);
++ }
++#endif
++
++ if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
++ write_cr2(this_cpu_read(nmi_cr2));
++ if (this_cpu_dec_return(nmi_state))
++ goto nmi_restart;
+ }
+ NOKPROBE_SYMBOL(do_nmi);
+
diff --git
a/debian/patches/bugfix/x86/0005-x86-nmi-64-Remove-asm-code-that-saves-cr2.patch
b/debian/patches/bugfix/x86/0005-x86-nmi-64-Remove-asm-code-that-saves-cr2.patch
new file mode 100644
index 0000000..0228968
--- /dev/null
+++
b/debian/patches/bugfix/x86/0005-x86-nmi-64-Remove-asm-code-that-saves-cr2.patch
@@ -0,0 +1,51 @@
+From: Andy Lutomirski <[email protected]>
+Date: Fri, 10 Jul 2015 12:03:34 -0700
+Subject: [PATCH 5/9] x86/nmi/64: Remove asm code that saves cr2
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=e7c2c90651fd54c3ca499fbb065ea5cbac30047d
+
+Now that do_nmi saves cr2, we don't need to save it in asm.
+
+This is a prerequisity for the fix for CVE-2015-3290.
+
+Cc: [email protected]
+Reviewed-by: Steven Rostedt <[email protected]>
+Acked-by: Borislav Petkov <[email protected]>
+Signed-off-by: Andy Lutomirski <[email protected]>
+[bwh: Backported to 4.0: adjust filename, context]
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 18 ------------------
+ 1 file changed, 18 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1654,29 +1654,11 @@ end_repeat_nmi:
+ call save_paranoid
+ DEFAULT_FRAME 0
+
+- /*
+- * Save off the CR2 register. If we take a page fault in the NMI then
+- * it could corrupt the CR2 value. If the NMI preempts a page fault
+- * handler before it was able to read the CR2 register, and then the
+- * NMI itself takes a page fault, the page fault that was preempted
+- * will read the information from the NMI page fault and not the
+- * origin fault. Save it off and restore it if it changes.
+- * Use the r12 callee-saved register.
+- */
+- movq %cr2, %r12
+-
+ /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
+ movq %rsp,%rdi
+ movq $-1,%rsi
+ call do_nmi
+
+- /* Did the NMI take a page fault? Restore cr2 if it did */
+- movq %cr2, %rcx
+- cmpq %rcx, %r12
+- je 1f
+- movq %r12, %cr2
+-1:
+-
+ testl %ebx,%ebx /* swapgs needed? */
+ jnz nmi_restore
+ nmi_swapgs:
diff --git
a/debian/patches/bugfix/x86/0006-x86-nmi-64-Switch-stacks-on-userspace-NMI-entry.patch
b/debian/patches/bugfix/x86/0006-x86-nmi-64-Switch-stacks-on-userspace-NMI-entry.patch
new file mode 100644
index 0000000..3654565
--- /dev/null
+++
b/debian/patches/bugfix/x86/0006-x86-nmi-64-Switch-stacks-on-userspace-NMI-entry.patch
@@ -0,0 +1,133 @@
+From: Andy Lutomirski <[email protected]>
+Date: Fri, 10 Jul 2015 11:35:31 -0700
+Subject: [PATCH 6/9] x86/nmi/64: Switch stacks on userspace NMI entry
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=4fb2a8d9cb0efcd7405f1ad105d7f3c764afe02f
+
+Returning to userspace is tricky: IRET can fail, and ESPFIX can
+rearrange the stack prior to IRET.
+
+The NMI nesting fixup relies on a precise stack layout and atomic
+IRET. Rather than trying to teach the NMI nesting fixup to handle
+ESPFIX and failed IRET, punt: run NMIs that came from user mode on
+the normal kernel stack.
+
+This will make some nested NMIs visible to C code, but the C code is
+okay with that.
+
+As a side effect, this should speed up perf: it eliminates an RDMSR
+when NMIs come from user mode.
+
+Fixes CVE-2015-3290.
+
+Cc: [email protected]
+Reviewed-by: Steven Rostedt <[email protected]>
+Reviewed-by: Borislav Petkov <[email protected]>
+Signed-off-by: Andy Lutomirski <[email protected]>
+[bwh: Backported to 4.0:
+ - Adjust filename, context
+ - s/restore_c_regs_and_iret/restore_args/
+ - Use kernel_stack + KERNEL_STACK_OFFSET instead of cpu_current_top_of_stack]
+[luto: Open-coded return path to avoid dependency on partial pt_regs details]
+Signed-off-by: Ben Hutchings <[email protected]>
+Signed-off-by: Andy Lutomirski <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 79 +++++++++++++++++++++++++++++++++++++++++++---
+ 1 file changed, 75 insertions(+), 4 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1475,19 +1475,90 @@ ENTRY(nmi)
+ * a nested NMI that updated the copy interrupt stack frame, a
+ * jump will be made to the repeat_nmi code that will handle the second
+ * NMI.
++ *
++ * However, espfix prevents us from directly returning to userspace
++ * with a single IRET instruction. Similarly, IRET to user mode
++ * can fault. We therefore handle NMIs from user space like
++ * other IST entries.
+ */
+
+ /* Use %rdx as out temp variable throughout */
+ pushq_cfi %rdx
+ CFI_REL_OFFSET rdx, 0
+
++ testb $3, CS-RIP+8(%rsp)
++ jz .Lnmi_from_kernel
++
++ /*
++ * NMI from user mode. We need to run on the thread stack, but we
++ * can't go through the normal entry paths: NMIs are masked, and
++ * we don't want to enable interrupts, because then we'll end
++ * up in an awkward situation in which IRQs are on but NMIs
++ * are off.
++ */
++
++ SWAPGS
++ cld
++ movq %rsp, %rdx
++ movq PER_CPU_VAR(kernel_stack), %rsp
++ addq $KERNEL_STACK_OFFSET, %rsp
++ pushq 5*8(%rdx) /* pt_regs->ss */
++ pushq 4*8(%rdx) /* pt_regs->rsp */
++ pushq 3*8(%rdx) /* pt_regs->flags */
++ pushq 2*8(%rdx) /* pt_regs->cs */
++ pushq 1*8(%rdx) /* pt_regs->rip */
++ pushq $-1 /* pt_regs->orig_ax */
++ pushq %rdi /* pt_regs->di */
++ pushq %rsi /* pt_regs->si */
++ pushq (%rdx) /* pt_regs->dx */
++ pushq %rcx /* pt_regs->cx */
++ pushq %rax /* pt_regs->ax */
++ pushq %r8 /* pt_regs->r8 */
++ pushq %r9 /* pt_regs->r9 */
++ pushq %r10 /* pt_regs->r10 */
++ pushq %r11 /* pt_regs->r11 */
++ pushq %rbx /* pt_regs->rbx */
++ pushq %rbp /* pt_regs->rbp */
++ pushq %r12 /* pt_regs->r12 */
++ pushq %r13 /* pt_regs->r13 */
++ pushq %r14 /* pt_regs->r14 */
++ pushq %r15 /* pt_regs->r15 */
++
++ /*
++ * At this point we no longer need to worry about stack damage
++ * due to nesting -- we're on the normal thread stack and we're
++ * done with the NMI stack.
++ */
++
++ movq %rsp, %rdi
++ movq $-1, %rsi
++ call do_nmi
++
++ /*
++ * Return back to user mode. We must *not* do the normal exit
++ * work, because we don't want to enable interrupts. Fortunately,
++ * do_nmi doesn't modify pt_regs.
++ */
++ SWAPGS
++
+ /*
+- * If %cs was not the kernel segment, then the NMI triggered in user
+- * space, which means it is definitely not nested.
++ * Open-code the entire return process for compatibility with varying
++ * register layouts across different kernel versions.
+ */
+- cmpl $__KERNEL_CS, 16(%rsp)
+- jne first_nmi
++ addq $6*8, %rsp /* skip bx, bp, and r12-r15 */
++ popq %r11 /* pt_regs->r11 */
++ popq %r10 /* pt_regs->r10 */
++ popq %r9 /* pt_regs->r9 */
++ popq %r8 /* pt_regs->r8 */
++ popq %rax /* pt_regs->ax */
++ popq %rcx /* pt_regs->cx */
++ popq %rdx /* pt_regs->dx */
++ popq %rsi /* pt_regs->si */
++ popq %rdi /* pt_regs->di */
++ addq $8, %rsp /* skip orig_ax */
++ INTERRUPT_RETURN
+
++.Lnmi_from_kernel:
+ /*
+ * Check the special variable on the stack to see if NMIs are
+ * executing.
diff --git
a/debian/patches/bugfix/x86/0007-x86-nmi-64-Improve-nested-NMI-comments.patch
b/debian/patches/bugfix/x86/0007-x86-nmi-64-Improve-nested-NMI-comments.patch
new file mode 100644
index 0000000..d69d5e3
--- /dev/null
+++
b/debian/patches/bugfix/x86/0007-x86-nmi-64-Improve-nested-NMI-comments.patch
@@ -0,0 +1,279 @@
+From: Andy Lutomirski <[email protected]>
+Date: Fri, 10 Jul 2015 17:13:26 -0700
+Subject: [PATCH 7/9] x86/nmi/64: Improve nested NMI comments
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=ed02eaa10579ffd480c3bda29701e658f17196e9
+
+I found the nested NMI documentation to be difficult to follow.
+Improve the comments.
+
+Cc: [email protected]
+Signed-off-by: Andy Lutomirski <[email protected]>
+[bwh: Backported to 4.0: adjust filename, context]
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 159 ++++++++++++++++++++++++++-------------------
+ arch/x86/kernel/nmi.c | 4 +-
+ 2 files changed, 93 insertions(+), 70 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1462,11 +1462,12 @@ ENTRY(nmi)
+ * If the variable is not set and the stack is not the NMI
+ * stack then:
+ * o Set the special variable on the stack
+- * o Copy the interrupt frame into a "saved" location on the stack
+- * o Copy the interrupt frame into a "copy" location on the stack
++ * o Copy the interrupt frame into an "outermost" location on the
++ * stack
++ * o Copy the interrupt frame into an "iret" location on the stack
+ * o Continue processing the NMI
+ * If the variable is set or the previous stack is the NMI stack:
+- * o Modify the "copy" location to jump to the repeate_nmi
++ * o Modify the "iret" location to jump to the repeat_nmi
+ * o return back to the first NMI
+ *
+ * Now on exit of the first NMI, we first clear the stack variable
+@@ -1560,18 +1561,60 @@ ENTRY(nmi)
+
+ .Lnmi_from_kernel:
+ /*
+- * Check the special variable on the stack to see if NMIs are
+- * executing.
++ * Here's what our stack frame will look like:
++ * +---------------------------------------------------------+
++ * | original SS |
++ * | original Return RSP |
++ * | original RFLAGS |
++ * | original CS |
++ * | original RIP |
++ * +---------------------------------------------------------+
++ * | temp storage for rdx |
++ * +---------------------------------------------------------+
++ * | "NMI executing" variable |
++ * +---------------------------------------------------------+
++ * | iret SS } Copied from "outermost" frame |
++ * | iret Return RSP } on each loop iteration; overwritten |
++ * | iret RFLAGS } by a nested NMI to force another |
++ * | iret CS } iteration if needed. |
++ * | iret RIP } |
++ * +---------------------------------------------------------+
++ * | outermost SS } initialized in first_nmi; |
++ * | outermost Return RSP } will not be changed before |
++ * | outermost RFLAGS } NMI processing is done. |
++ * | outermost CS } Copied to "iret" frame on each |
++ * | outermost RIP } iteration. |
++ * +---------------------------------------------------------+
++ * | pt_regs |
++ * +---------------------------------------------------------+
++ *
++ * The "original" frame is used by hardware. Before re-enabling
++ * NMIs, we need to be done with it, and we need to leave enough
++ * space for the asm code here.
++ *
++ * We return by executing IRET while RSP points to the "iret" frame.
++ * That will either return for real or it will loop back into NMI
++ * processing.
++ *
++ * The "outermost" frame is copied to the "iret" frame on each
++ * iteration of the loop, so each iteration starts with the "iret"
++ * frame pointing to the final return target.
++ */
++
++ /*
++ * Determine whether we're a nested NMI.
++ *
++ * First check "NMI executing". If it's set, then we're nested.
++ * This will not detect if we interrupted an outer NMI just
++ * before IRET.
+ */
+ cmpl $1, -8(%rsp)
+ je nested_nmi
+
+ /*
+- * Now test if the previous stack was an NMI stack.
+- * We need the double check. We check the NMI stack to satisfy the
+- * race when the first NMI clears the variable before returning.
+- * We check the variable because the first NMI could be in a
+- * breakpoint routine using a breakpoint stack.
++ * Now test if the previous stack was an NMI stack. This covers
++ * the case where we interrupt an outer NMI after it clears
++ * "NMI executing" but before IRET.
+ */
+ lea 6*8(%rsp), %rdx
+ /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp))
*/
+@@ -1588,9 +1631,11 @@ ENTRY(nmi)
+
+ nested_nmi:
+ /*
+- * Do nothing if we interrupted the fixup in repeat_nmi.
+- * It's about to repeat the NMI handler, so we are fine
+- * with ignoring this one.
++ * If we interrupted an NMI that is between repeat_nmi and
++ * end_repeat_nmi, then we must not modify the "iret" frame
++ * because it's being written by the outer NMI. That's okay:
++ * the outer NMI handler is about to call do_nmi anyway,
++ * so we can just resume the outer NMI.
+ */
+ movq $repeat_nmi, %rdx
+ cmpq 8(%rsp), %rdx
+@@ -1600,7 +1645,10 @@ nested_nmi:
+ ja nested_nmi_out
+
+ 1:
+- /* Set up the interrupted NMIs stack to jump to repeat_nmi */
++ /*
++ * Modify the "iret" frame to point to repeat_nmi, forcing another
++ * iteration of NMI handling.
++ */
+ leaq -1*8(%rsp), %rdx
+ movq %rdx, %rsp
+ CFI_ADJUST_CFA_OFFSET 1*8
+@@ -1619,60 +1667,23 @@ nested_nmi_out:
+ popq_cfi %rdx
+ CFI_RESTORE rdx
+
+- /* No need to check faults here */
++ /* We are returning to kernel mode, so this cannot result in a fault. */
+ INTERRUPT_RETURN
+
+ CFI_RESTORE_STATE
+ first_nmi:
+- /*
+- * Because nested NMIs will use the pushed location that we
+- * stored in rdx, we must keep that space available.
+- * Here's what our stack frame will look like:
+- * +-------------------------+
+- * | original SS |
+- * | original Return RSP |
+- * | original RFLAGS |
+- * | original CS |
+- * | original RIP |
+- * +-------------------------+
+- * | temp storage for rdx |
+- * +-------------------------+
+- * | NMI executing variable |
+- * +-------------------------+
+- * | copied SS |
+- * | copied Return RSP |
+- * | copied RFLAGS |
+- * | copied CS |
+- * | copied RIP |
+- * +-------------------------+
+- * | Saved SS |
+- * | Saved Return RSP |
+- * | Saved RFLAGS |
+- * | Saved CS |
+- * | Saved RIP |
+- * +-------------------------+
+- * | pt_regs |
+- * +-------------------------+
+- *
+- * The saved stack frame is used to fix up the copied stack frame
+- * that a nested NMI may change to make the interrupted NMI iret jump
+- * to the repeat_nmi. The original stack frame and the temp storage
+- * is also used by nested NMIs and can not be trusted on exit.
+- */
+- /* Do not pop rdx, nested NMIs will corrupt that part of the stack */
++ /* Restore rdx. */
+ movq (%rsp), %rdx
+ CFI_RESTORE rdx
+
+- /* Set the NMI executing variable on the stack. */
++ /* Set "NMI executing" on the stack. */
+ pushq_cfi $1
+
+- /*
+- * Leave room for the "copied" frame
+- */
++ /* Leave room for the "iret" frame */
+ subq $(5*8), %rsp
+ CFI_ADJUST_CFA_OFFSET 5*8
+
+- /* Copy the stack frame to the Saved frame */
++ /* Copy the "original" frame to the "outermost" frame */
+ .rept 5
+ pushq_cfi 11*8(%rsp)
+ .endr
+@@ -1680,6 +1691,7 @@ first_nmi:
+
+ /* Everything up to here is safe from nested NMIs */
+
++repeat_nmi:
+ /*
+ * If there was a nested NMI, the first NMI's iret will return
+ * here. But NMIs are still enabled and we can take another
+@@ -1688,16 +1700,21 @@ first_nmi:
+ * it will just return, as we are about to repeat an NMI anyway.
+ * This makes it safe to copy to the stack frame that a nested
+ * NMI will update.
+- */
+-repeat_nmi:
+- /*
+- * Update the stack variable to say we are still in NMI (the update
+- * is benign for the non-repeat case, where 1 was pushed just above
+- * to this very stack slot).
++ *
++ * RSP is pointing to "outermost RIP". gsbase is unknown, but, if
++ * we're repeating an NMI, gsbase has the same value that it had on
++ * the first iteration. paranoid_entry will load the kernel
++ * gsbase if needed before we call do_nmi.
++ *
++ * Set "NMI executing" in case we came back here via IRET.
+ */
+ movq $1, 10*8(%rsp)
+
+- /* Make another copy, this one may be modified by nested NMIs */
++ /*
++ * Copy the "outermost" frame to the "iret" frame. NMIs that nest
++ * here must not modify the "iret" frame while we're writing to
++ * it or it will end up containing garbage.
++ */
+ addq $(10*8), %rsp
+ CFI_ADJUST_CFA_OFFSET -10*8
+ .rept 5
+@@ -1708,9 +1725,9 @@ repeat_nmi:
+ end_repeat_nmi:
+
+ /*
+- * Everything below this point can be preempted by a nested
+- * NMI if the first NMI took an exception and reset our iret stack
+- * so that we repeat another NMI.
++ * Everything below this point can be preempted by a nested NMI.
++ * If this happens, then the inner NMI will change the "iret"
++ * frame to point back to repeat_nmi.
+ */
+ pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
+ subq $ORIG_RAX-R15, %rsp
+@@ -1735,11 +1752,17 @@ end_repeat_nmi:
+ nmi_swapgs:
+ SWAPGS_UNSAFE_STACK
+ nmi_restore:
+- /* Pop the extra iret frame at once */
++
+ RESTORE_ALL 6*8
+
+- /* Clear the NMI executing stack variable */
++ /* Clear "NMI executing". */
+ movq $0, 5*8(%rsp)
++
++ /*
++ * INTERRUPT_RETURN reads the "iret" frame and exits the NMI
++ * stack in a single instruction. We are returning to kernel
++ * mode, so this cannot result in a fault.
++ */
+ jmp irq_return
+ CFI_ENDPROC
+ END(nmi)
+--- a/arch/x86/kernel/nmi.c
++++ b/arch/x86/kernel/nmi.c
+@@ -408,8 +408,8 @@ static void default_do_nmi(struct pt_reg
+ NOKPROBE_SYMBOL(default_do_nmi);
+
+ /*
+- * NMIs can hit breakpoints which will cause it to lose its NMI context
+- * with the CPU when the breakpoint or page fault does an IRET.
++ * NMIs can page fault or hit breakpoints which will cause it to lose
++ * its NMI context with the CPU when the breakpoint or page fault does an
IRET.
+ *
+ * As a result, NMIs can nest if NMIs get unmasked due an IRET during
+ * NMI processing. On x86_64, the asm glue protects us from nested NMIs
diff --git
a/debian/patches/bugfix/x86/0008-x86-nmi-64-Reorder-nested-NMI-checks.patch
b/debian/patches/bugfix/x86/0008-x86-nmi-64-Reorder-nested-NMI-checks.patch
new file mode 100644
index 0000000..196dd15
--- /dev/null
+++ b/debian/patches/bugfix/x86/0008-x86-nmi-64-Reorder-nested-NMI-checks.patch
@@ -0,0 +1,83 @@
+From: Andy Lutomirski <[email protected]>
+Date: Sun, 12 Jul 2015 20:59:57 -0700
+Subject: [PATCH 8/9] x86/nmi/64: Reorder nested NMI checks
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=b7dcb27674b28ca49b710e95da74c44d32154bed
+
+Check the repeat_nmi .. end_repeat_nmi special case first. The next
+patch will rework the RSP check and, as a side effect, the RSP check
+will no longer detect repeat_nmi .. end_repeat_nmi, so we'll need
+this ordering of the checks.
+
+Note: this is more subtle than it appears. The check for repeat_nmi
+.. end_repeat_nmi jumps straight out of the NMI code instead of
+adjusting the "iret" frame to force a repeat. This is necessary,
+because the code between repeat_nmi and end_repeat_nmi sets "NMI
+executing" and then writes to the "iret" frame itself. If a nested
+NMI comes in and modifies the "iret" frame while repeat_nmi is also
+modifying it, we'll end up with garbage. The old code got this
+right, as does the new code, but the new code is a bit more
+explicit.
+
+If we were to move the check right after the "NMI executing" check,
+then we'd get it wrong and have random crashes.
+
+This is a prerequisite for the fix for CVE-2015-3291.
+
+Cc: [email protected]
+Signed-off-by: Andy Lutomirski <[email protected]>
+[bwh: Backported to 4.0: adjust filename, spacing]
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 34 ++++++++++++++++++----------------
+ 1 file changed, 18 insertions(+), 16 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1604,7 +1604,24 @@ ENTRY(nmi)
+ /*
+ * Determine whether we're a nested NMI.
+ *
+- * First check "NMI executing". If it's set, then we're nested.
++ * If we interrupted kernel code between repeat_nmi and
++ * end_repeat_nmi, then we are a nested NMI. We must not
++ * modify the "iret" frame because it's being written by
++ * the outer NMI. That's okay: the outer NMI handler is
++ * about to about to call do_nmi anyway, so we can just
++ * resume the outer NMI.
++ */
++
++ movq $repeat_nmi, %rdx
++ cmpq 8(%rsp), %rdx
++ ja 1f
++ movq $end_repeat_nmi, %rdx
++ cmpq 8(%rsp), %rdx
++ ja nested_nmi_out
++1:
++
++ /*
++ * Now check "NMI executing". If it's set, then we're nested.
+ * This will not detect if we interrupted an outer NMI just
+ * before IRET.
+ */
+@@ -1631,21 +1648,6 @@ ENTRY(nmi)
+
+ nested_nmi:
+ /*
+- * If we interrupted an NMI that is between repeat_nmi and
+- * end_repeat_nmi, then we must not modify the "iret" frame
+- * because it's being written by the outer NMI. That's okay:
+- * the outer NMI handler is about to call do_nmi anyway,
+- * so we can just resume the outer NMI.
+- */
+- movq $repeat_nmi, %rdx
+- cmpq 8(%rsp), %rdx
+- ja 1f
+- movq $end_repeat_nmi, %rdx
+- cmpq 8(%rsp), %rdx
+- ja nested_nmi_out
+-
+-1:
+- /*
+ * Modify the "iret" frame to point to repeat_nmi, forcing another
+ * iteration of NMI handling.
+ */
diff --git
a/debian/patches/bugfix/x86/0009-x86-nmi-64-Use-DF-to-avoid-userspace-RSP-confusing-n.patch
b/debian/patches/bugfix/x86/0009-x86-nmi-64-Use-DF-to-avoid-userspace-RSP-confusing-n.patch
new file mode 100644
index 0000000..1795485
--- /dev/null
+++
b/debian/patches/bugfix/x86/0009-x86-nmi-64-Use-DF-to-avoid-userspace-RSP-confusing-n.patch
@@ -0,0 +1,86 @@
+From: Andy Lutomirski <[email protected]>
+Date: Fri, 10 Jul 2015 17:25:53 -0700
+Subject: [PATCH 9/9] x86/nmi/64: Use DF to avoid userspace RSP confusing
+ nested NMI detection
+Origin:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/?commit=dc68c0f2ec634b2cfecf879235564da58d422cee
+
+We have a tricky bug in the nested NMI code: if we see RSP pointing
+to the NMI stack on NMI entry from kernel mode, we assume that we
+are executing a nested NMI.
+
+This isn't quite true. A malicious userspace program can point RSP
+at the NMI stack, issue SYSCALL, and arrange for an NMI to happen
+while RSP is still pointing at the NMI stack.
+
+Fix it with a sneaky trick. Set DF in the region of code that the RSP
+check is intended to detect. IRET will clear DF atomically.
+
+(Note: other than paravirt, there's little need for all this complexity.
+ We could check RIP instead of RSP.)
+
+Fixes CVE-2015-3291.
+
+Cc: [email protected]
+Reviewed-by: Steven Rostedt <[email protected]>
+Signed-off-by: Andy Lutomirski <[email protected]>
+[bwh: Backported to 4.0: adjust filename, context]
+Signed-off-by: Ben Hutchings <[email protected]>
+---
+ arch/x86/kernel/entry_64.S | 29 +++++++++++++++++++++++++----
+ 1 file changed, 25 insertions(+), 4 deletions(-)
+
+--- a/arch/x86/kernel/entry_64.S
++++ b/arch/x86/kernel/entry_64.S
+@@ -1631,7 +1631,14 @@ ENTRY(nmi)
+ /*
+ * Now test if the previous stack was an NMI stack. This covers
+ * the case where we interrupt an outer NMI after it clears
+- * "NMI executing" but before IRET.
++ * "NMI executing" but before IRET. We need to be careful, though:
++ * there is one case in which RSP could point to the NMI stack
++ * despite there being no NMI active: naughty userspace controls
++ * RSP at the very beginning of the SYSCALL targets. We can
++ * pull a fast one on naughty userspace, though: we program
++ * SYSCALL to mask DF, so userspace cannot cause DF to be set
++ * if it controls the kernel's RSP. We set DF before we clear
++ * "NMI executing".
+ */
+ lea 6*8(%rsp), %rdx
+ /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp))
*/
+@@ -1642,10 +1649,16 @@ ENTRY(nmi)
+ cmpq %rdx, 4*8(%rsp)
+ /* If it is below the NMI stack, it is a normal NMI */
+ jb first_nmi
+- /* Ah, it is within the NMI stack, treat it as nested */
++
++ /* Ah, it is within the NMI stack. */
++
++ testb $(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp)
++ jz first_nmi /* RSP was user controlled. */
+
+ CFI_REMEMBER_STATE
+
++ /* This is a nested NMI. */
++
+ nested_nmi:
+ /*
+ * Modify the "iret" frame to point to repeat_nmi, forcing another
+@@ -1757,8 +1770,16 @@ nmi_restore:
+
+ RESTORE_ALL 6*8
+
+- /* Clear "NMI executing". */
+- movq $0, 5*8(%rsp)
++ /*
++ * Clear "NMI executing". Set DF first so that we can easily
++ * distinguish the remaining code between here and IRET from
++ * the SYSCALL entry and exit paths. On a native kernel, we
++ * could just inspect RIP, but, on paravirt kernels,
++ * INTERRUPT_RETURN can translate into a jump into a
++ * hypercall page.
++ */
++ std
++ movq $0, 5*8(%rsp) /* clear "NMI executing" */
+
+ /*
+ * INTERRUPT_RETURN reads the "iret" frame and exits the NMI
diff --git a/debian/patches/series b/debian/patches/series
index 2476556..9f47b21 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -81,3 +81,13 @@
bugfix/all/stable-3.19.8-ckt2.patch
bugfix/all/stable-3.19.8-ckt3.patch
bugfix/all/stable-3.19.8-ckt4.patch
+
+# NMI security fixes
+bugfix/x86/0001-x86-asm-entry-64-Fold-the-test_in_nmi-macro-into-its.patch
+bugfix/x86/0002-x86-asm-entry-64-Remove-a-redundant-jump.patch
+bugfix/x86/0004-x86-nmi-Enable-nested-do_nmi-handling-for-64-bit-ker.patch
+bugfix/x86/0005-x86-nmi-64-Remove-asm-code-that-saves-cr2.patch
+bugfix/x86/0006-x86-nmi-64-Switch-stacks-on-userspace-NMI-entry.patch
+bugfix/x86/0007-x86-nmi-64-Improve-nested-NMI-comments.patch
+bugfix/x86/0008-x86-nmi-64-Reorder-nested-NMI-checks.patch
+bugfix/x86/0009-x86-nmi-64-Use-DF-to-avoid-userspace-RSP-confusing-n.patch
--
To view, visit https://gerrit.wikimedia.org/r/226703
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: merged
Gerrit-Change-Id: I1f42ee028cfccbe857626af4f892c97261d1b32f
Gerrit-PatchSet: 1
Gerrit-Project: operations/debs/linux
Gerrit-Branch: master
Gerrit-Owner: Muehlenhoff <[email protected]>
Gerrit-Reviewer: Muehlenhoff <[email protected]>
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