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author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-12-27 11:48:50 -0800 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2017-12-27 20:59:41 +0100 |
commit | ac461122c88a10b7d775de2f56467f097c9e627a (patch) | |
tree | 2ab05096d98babdb99396330975b9793de81eb76 | |
parent | 7ac139eaa6bbdb07c547b6916a808eab3897e0e3 (diff) | |
download | linux-stable-ac461122c88a10b7d775de2f56467f097c9e627a.tar.gz linux-stable-ac461122c88a10b7d775de2f56467f097c9e627a.tar.bz2 linux-stable-ac461122c88a10b7d775de2f56467f097c9e627a.zip |
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 <achirvasub@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.LFD.2.21.1712271143180.8572@i7.lan
-rw-r--r-- | arch/x86/kernel/machine_kexec_32.c | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c index 00bc751c861c..edfede768688 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, |