From 04d1d281dcfe683a53cddfab8371fc8bb302b069 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Tue, 23 Feb 2016 13:19:29 -0800 Subject: [PATCH] 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 Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/3e36be110724896e32a4a1fe73bacb349d3cba94.1456262295.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/entry/entry_32.S | 1 + 1 file changed, 1 insertion(+) 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) */ -- 2.30.2