From 2854d767135c3ca131d8658f5b47974d7b067d3b Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 31 Oct 2014 18:08:45 -0700 Subject: 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 Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski Signed-off-by: Linus Torvalds Signed-off-by: Jiri Slaby --- arch/x86/ia32/ia32entry.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 711de084ab57..92a2e9333620 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: -- cgit v1.2.3