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authorAndy Lutomirski <luto@amacapital.net>2014-10-31 18:08:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-31 18:47:09 -0700
commit653bc77af60911ead1f423e588f54fc2547c4957 (patch)
treec1e404d37868318063fcb6f57d40346b0c1a131d
parent32e8fd2f8eac3262e7000d9a219d70ace10e0adf (diff)
x86_64, entry: Fix out of bounds read on sysenter
Rusty noticed a Really Bad Bug (tm) in my NT fix. The entry code reads out of bounds, causing the NT fix to be unreliable. But, and this is much, much worse, if your stack is somehow just below the top of the direct map (or a hole), you read out of bounds and crash. Excerpt from the crash: [ 1.129513] RSP: 0018:ffff88001da4bf88 EFLAGS: 00010296 2b:* f7 84 24 90 00 00 00 testl $0x4000,0x90(%rsp) That read is deterministically above the top of the stack. I thought I even single-stepped through this code when I wrote it to check the offset, but I clearly screwed it up. Fixes: 8c7aa698baca ("x86_64, entry: Filter RFLAGS.NT on entry from userspace") Reported-by: Rusty Russell <rusty@ozlabs.org> Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/x86/ia32/ia32entry.S2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 8ffba18395c8..ffe71228fc10 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -157,7 +157,7 @@ ENTRY(ia32_sysenter_target)
* ourselves. To save a few cycles, we can check whether
* NT was set instead of doing an unconditional popfq.
*/
- testl $X86_EFLAGS_NT,EFLAGS(%rsp) /* saved EFLAGS match cpu */
+ testl $X86_EFLAGS_NT,EFLAGS-ARGOFFSET(%rsp)
jnz sysenter_fix_flags
sysenter_flags_fixed: