[PATCH v2 3/3] x86/entry: Clear registers for compat syscalls

[Dan Williams]

From: Andi Kleen <ak@xxxxxxxxxxxxxxx>

At entry userspace may have populated registers with values that could
be useful in a speculative execution attack. Clear them to minimize the
kernel's attack surface.

[djbw: rename the macro, only clear the extra registers]
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 arch/x86/entry/entry_64_compat.S |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 98d5358e4041..f55b018a580b 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -95,6 +95,7 @@ ENTRY(entry_SYSENTER_compat)
 	pushq   $0			/* pt_regs->r14 = 0 */
 	pushq   $0			/* pt_regs->r15 = 0 */
 	cld
+	CLEAR_EXTRA_REGS_NOSPEC
 
 	/*
 	 * SYSENTER doesn't filter flags, so we need to clear NT and AC
@@ -223,6 +224,7 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
 	pushq   $0			/* pt_regs->r13 = 0 */
 	pushq   $0			/* pt_regs->r14 = 0 */
 	pushq   $0			/* pt_regs->r15 = 0 */
+	CLEAR_EXTRA_REGS_NOSPEC
 
 	/*
 	 * User mode is traced as though IRQs are on, and SYSENTER
@@ -348,6 +350,7 @@ ENTRY(entry_INT80_compat)
 	pushq   %r14                    /* pt_regs->r14 */
 	pushq   %r15                    /* pt_regs->r15 */
 	cld
+	CLEAR_EXTRA_REGS_NOSPEC
 
 	/*
 	 * User mode is traced as though IRQs are on, and the interrupt