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authorAndy Lutomirski <luto@kernel.org>2016-02-23 13:19:29 -0800
committerIngo Molnar <mingo@kernel.org>2016-02-24 08:43:04 +0100
commit04d1d281dcfe683a53cddfab8371fc8bb302b069 (patch)
tree8622a05e522fea41d855fa8b0177777203fb491d /arch
parentdd71a17b1193dd4a4c35ecd0ba227aac3d110836 (diff)
x86/entry/32: Add an ASM_CLAC to entry_SYSENTER_32
Both before and after 5f310f739b4c ("x86/entry/32: Re-implement SYSENTER using the new C path"), we relied on a uaccess very early in the SYSENTER path to clear AC. After that change, though, we can potentially make it all the way into C code with AC set, which enlarges the attack surface for SMAP bypass by doing SYSENTER with AC set. Strengthen the SMAP protection by addding the missing ASM_CLAC right at the beginning. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/3e36be110724896e32a4a1fe73bacb349d3cba94.1456262295.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/entry/entry_32.S1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 77d8c5112900..bb3e376d0f33 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -294,6 +294,7 @@ sysenter_past_esp:
pushl $__USER_DS /* pt_regs->ss */
pushl %ebp /* pt_regs->sp (stashed in bp) */
pushfl /* pt_regs->flags (except IF = 0) */
+ ASM_CLAC /* Clear AC after saving FLAGS */
orl $X86_EFLAGS_IF, (%esp) /* Fix IF */
pushl $__USER_CS /* pt_regs->cs */
pushl $0 /* pt_regs->ip = 0 (placeholder) */