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Subject[PATCH 3/3] x86/entry: Clear registers for compat syscalls
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Date
From: Andi Kleen <ak@linux.intel.com>

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@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
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
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