[PATCH 4.9 64/92] x86/syscall: Sanitize syscall table de-references under speculation

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

--

From: Dan Williams 


(cherry picked from commit 2fbd7af5af8665d18bcefae3e9700be07e22b681)

The syscall table base is a user controlled function pointer in kernel
space. Use array_index_nospec() to prevent any out of bounds speculation.

While retpoline prevents speculating into a userspace directed target it
does not stop the pointer de-reference, the concern is leaking memory
relative to the syscall table base, by observing instruction cache
behavior.

Reported-by: Linus Torvalds 
Signed-off-by: Dan Williams 
Signed-off-by: Thomas Gleixner 
Cc: linux-a...@vger.kernel.org
Cc: kernel-harden...@lists.openwall.com
Cc: gre...@linuxfoundation.org
Cc: Andy Lutomirski 
Cc: a...@linux.intel.com
Link: 
https://lkml.kernel.org/r/151727417984.33451.1216731042505722161.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman 
---
 arch/x86/entry/common.c |5 -
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -20,6 +20,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 
 #include 
@@ -277,7 +278,8 @@ __visible void do_syscall_64(struct pt_r
 * regs->orig_ax, which changes the behavior of some syscalls.
 */
if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
-   regs->ax = sys_call_table[nr & __SYSCALL_MASK](
+   nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
+   regs->ax = sys_call_table[nr](
regs->di, regs->si, regs->dx,
regs->r10, regs->r8, regs->r9);
}
@@ -313,6 +315,7 @@ static __always_inline void do_syscall_3
}
 
if (likely(nr < IA32_NR_syscalls)) {
+   nr = array_index_nospec(nr, IA32_NR_syscalls);
/*
 * It's possible that a 32-bit syscall implementation
 * takes a 64-bit parameter but nonetheless assumes that

[PATCH 4.9 64/92] x86/syscall: Sanitize syscall table de-references under speculation

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

--

From: Dan Williams 


(cherry picked from commit 2fbd7af5af8665d18bcefae3e9700be07e22b681)

The syscall table base is a user controlled function pointer in kernel
space. Use array_index_nospec() to prevent any out of bounds speculation.

While retpoline prevents speculating into a userspace directed target it
does not stop the pointer de-reference, the concern is leaking memory
relative to the syscall table base, by observing instruction cache
behavior.

Reported-by: Linus Torvalds 
Signed-off-by: Dan Williams 
Signed-off-by: Thomas Gleixner 
Cc: linux-a...@vger.kernel.org
Cc: kernel-harden...@lists.openwall.com
Cc: gre...@linuxfoundation.org
Cc: Andy Lutomirski 
Cc: a...@linux.intel.com
Link: 
https://lkml.kernel.org/r/151727417984.33451.1216731042505722161.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: David Woodhouse 
Signed-off-by: Greg Kroah-Hartman 
---
 arch/x86/entry/common.c |5 -
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -20,6 +20,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 
 #include 
@@ -277,7 +278,8 @@ __visible void do_syscall_64(struct pt_r
 * regs->orig_ax, which changes the behavior of some syscalls.
 */
if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
-   regs->ax = sys_call_table[nr & __SYSCALL_MASK](
+   nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
+   regs->ax = sys_call_table[nr](
regs->di, regs->si, regs->dx,
regs->r10, regs->r8, regs->r9);
}
@@ -313,6 +315,7 @@ static __always_inline void do_syscall_3
}
 
if (likely(nr < IA32_NR_syscalls)) {
+   nr = array_index_nospec(nr, IA32_NR_syscalls);
/*
 * It's possible that a 32-bit syscall implementation
 * takes a 64-bit parameter but nonetheless assumes that