Commit-ID: ac461122c88a10b7d775de2f56467f097c9e627a
Gitweb: https://git.kernel.org/tip/ac461122c88a10b7d775de2f56467f097c9e627a
Author: Linus Torvalds <torva...@linux-foundation.org>
AuthorDate: Wed, 27 Dec 2017 11:48:50 -0800
Committer: Thomas Gleixner <t...@linutronix.de>
CommitDate: Wed, 27 Dec 2017 20:59:41 +0100
x86-32: Fix kexec with stack canary (CONFIG_CC_STACKPROTECTOR)
Commit e802a51ede91 ("x86/idt: Consolidate IDT invalidation") cleaned up
and unified the IDT invalidation that existed in a couple of places. It
changed no actual real code.
Despite not changing any actual real code, it _did_ change code generation:
by implementing the common idt_invalidate() function in
archx86/kernel/idt.c, it made the use of the function in
arch/x86/kernel/machine_kexec_32.c be a real function call rather than an
(accidental) inlining of the function.
That, in turn, exposed two issues:
- in load_segments(), we had incorrectly reset all the segment
registers, which then made the stack canary load (which gcc does
using offset of %gs) cause a trap. Instead of %gs pointing to the
stack canary, it will be the normal zero-based kernel segment, and
the stack canary load will take a page fault at address 0x14.
- to make this even harder to debug, we had invalidated the GDT just
before calling idt_invalidate(), which meant that the fault happened
with an invalid GDT, which in turn causes a triple fault and
immediate reboot.
Fix this by
(a) not reloading the special segments in load_segments(). We currently
don't do any percpu accesses (which would require %fs on x86-32) in
this area, but there's no reason to think that we might not want to
do them, and like %gs, it's pointless to break it.
(b) doing idt_invalidate() before invalidating the GDT, to keep things
at least _slightly_ more debuggable for a bit longer. Without a
IDT, traps will not work. Without a GDT, traps also will not work,
but neither will any segment loads etc. So in a very real sense,
the GDT is even more core than the IDT.
Fixes: e802a51ede91 ("x86/idt: Consolidate IDT invalidation")
Reported-and-tested-by: Alexandru Chirvasitu <achirva...@gmail.com>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: Denys Vlasenko <dvlas...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Brian Gerst <brge...@gmail.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: sta...@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.lfd.2.21.1712271143180.8...@i7.lan
---
arch/x86/kernel/machine_kexec_32.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/x86/kernel/machine_kexec_32.c
b/arch/x86/kernel/machine_kexec_32.c
index 00bc751..edfede7 100644
--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -48,8 +48,6 @@ static void load_segments(void)
"\tmovl $"STR(__KERNEL_DS)",%%eax\n"
"\tmovl %%eax,%%ds\n"
"\tmovl %%eax,%%es\n"
- "\tmovl %%eax,%%fs\n"
- "\tmovl %%eax,%%gs\n"
"\tmovl %%eax,%%ss\n"
: : : "eax", "memory");
#undef STR
@@ -232,8 +230,8 @@ void machine_kexec(struct kimage *image)
* The gdt & idt are now invalid.
* If you want to load them you must set up your own idt & gdt.
*/
- set_gdt(phys_to_virt(0), 0);
idt_invalidate(phys_to_virt(0));
+ set_gdt(phys_to_virt(0), 0);
/* now call it */
image->start = relocate_kernel_ptr((unsigned long)image->head,
