Messages in this thread Patch in this message | | | Date | Wed, 24 Feb 2016 21:53:53 -0800 | From | tip-bot for Andy Lutomirski <> | Subject | [tip:x86/urgent] x86/entry/32: Add an ASM_CLAC to entry_SYSENTER_32 |
| |
Commit-ID: 04d1d281dcfe683a53cddfab8371fc8bb302b069 Gitweb: http://git.kernel.org/tip/04d1d281dcfe683a53cddfab8371fc8bb302b069 Author: Andy Lutomirski <luto@kernel.org> AuthorDate: Tue, 23 Feb 2016 13:19:29 -0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 24 Feb 2016 08:43:04 +0100
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> --- 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 77d8c51..bb3e376 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) */
| |