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authorAndy Lutomirski <luto@amacapital.net>2014-10-31 18:08:45 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-14 08:47:54 -0800
commit621be26198eba8272e702ccbd27648c6aae01bc0 (patch)
treee633dee0e417e499482bd340520f8e4e792701b4 /arch
parentb1a9c1e7969403e9d31ac335f4ebb43c9461ab59 (diff)
x86_64, entry: Fix out of bounds read on sysenter
commit 653bc77af60911ead1f423e588f54fc2547c4957 upstream. 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> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-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 22417f6fc3ab..c9305ef1d411 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: