[PATCH 4.15 062/163] x86/entry/64: Introduce the PUSH_AND_CLEAN_REGS macro

From: Greg Kroah-Hartman
Date: Wed Feb 21 2018 - 08:10:06 EST


4.15-stable review patch. If anyone has any objections, please let me know.

------------------

From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>

commit 3f01daecd545e818098d84fd1ad43e19a508d705 upstream.

Those instances where ALLOC_PT_GPREGS_ON_STACK is called just before
SAVE_AND_CLEAR_REGS can trivially be replaced by PUSH_AND_CLEAN_REGS.
This macro uses PUSH instead of MOV and should therefore be faster, at
least on newer CPUs.

Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: dan.j.williams@xxxxxxxxx
Link: http://lkml.kernel.org/r/20180211104949.12992-5-linux@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
arch/x86/entry/calling.h | 36 ++++++++++++++++++++++++++++++++++++
arch/x86/entry/entry_64.S | 6 ++----
2 files changed, 38 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -137,6 +137,42 @@ For 32-bit we have the following convent
UNWIND_HINT_REGS offset=\offset
.endm

+ .macro PUSH_AND_CLEAR_REGS
+ /*
+ * Push registers and sanitize registers of values that a
+ * speculation attack might otherwise want to exploit. The
+ * lower registers are likely clobbered well before they
+ * could be put to use in a speculative execution gadget.
+ * Interleave XOR with PUSH for better uop scheduling:
+ */
+ pushq %rdi /* pt_regs->di */
+ pushq %rsi /* pt_regs->si */
+ pushq %rdx /* pt_regs->dx */
+ pushq %rcx /* pt_regs->cx */
+ pushq %rax /* pt_regs->ax */
+ pushq %r8 /* pt_regs->r8 */
+ xorq %r8, %r8 /* nospec r8 */
+ pushq %r9 /* pt_regs->r9 */
+ xorq %r9, %r9 /* nospec r9 */
+ pushq %r10 /* pt_regs->r10 */
+ xorq %r10, %r10 /* nospec r10 */
+ pushq %r11 /* pt_regs->r11 */
+ xorq %r11, %r11 /* nospec r11*/
+ pushq %rbx /* pt_regs->rbx */
+ xorl %ebx, %ebx /* nospec rbx*/
+ pushq %rbp /* pt_regs->rbp */
+ xorl %ebp, %ebp /* nospec rbp*/
+ pushq %r12 /* pt_regs->r12 */
+ xorq %r12, %r12 /* nospec r12*/
+ pushq %r13 /* pt_regs->r13 */
+ xorq %r13, %r13 /* nospec r13*/
+ pushq %r14 /* pt_regs->r14 */
+ xorq %r14, %r14 /* nospec r14*/
+ pushq %r15 /* pt_regs->r15 */
+ xorq %r15, %r15 /* nospec r15*/
+ UNWIND_HINT_REGS
+ .endm
+
.macro POP_REGS pop_rdi=1 skip_r11rcx=0
popq %r15
popq %r14
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -564,8 +564,7 @@ END(irq_entries_start)
call switch_to_thread_stack
1:

- ALLOC_PT_GPREGS_ON_STACK
- SAVE_AND_CLEAR_REGS
+ PUSH_AND_CLEAR_REGS
ENCODE_FRAME_POINTER

testb $3, CS(%rsp)
@@ -1112,8 +1111,7 @@ ENTRY(xen_failsafe_callback)
addq $0x30, %rsp
UNWIND_HINT_IRET_REGS
pushq $-1 /* orig_ax = -1 => not a system call */
- ALLOC_PT_GPREGS_ON_STACK
- SAVE_AND_CLEAR_REGS
+ PUSH_AND_CLEAR_REGS
ENCODE_FRAME_POINTER
jmp error_exit
END(xen_failsafe_callback)