Avoid redundant load of %r11 (it is already loaded a few instructions before).
Do not needlessly increment %rsp - we are going to return to userspace
via SYSRET, this insn doesn't use stack for return.
Changes since v1: added a comment
Signed-off-by: Denys Vlasenko <[email protected]>
CC: Linus Torvalds <[email protected]>
CC: Steven Rostedt <[email protected]>
CC: Ingo Molnar <[email protected]>
CC: Borislav Petkov <[email protected]>
CC: "H. Peter Anvin" <[email protected]>
CC: Andy Lutomirski <[email protected]>
CC: Oleg Nesterov <[email protected]>
CC: Frederic Weisbecker <[email protected]>
CC: Alexei Starovoitov <[email protected]>
CC: Will Drewry <[email protected]>
CC: Kees Cook <[email protected]>
CC: [email protected]
CC: [email protected]
---
arch/x86/include/asm/calling.h | 3 +++
arch/x86/kernel/entry_64.S | 6 +++---
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 3374235..f1a962f 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -176,6 +176,9 @@ For 32-bit we have the following conventions - kernel is built with
.macro RESTORE_C_REGS_EXCEPT_RCX
RESTORE_C_REGS_HELPER 1,0,1,1,1
.endm
+ .macro RESTORE_C_REGS_EXCEPT_R11
+ RESTORE_C_REGS_HELPER 1,1,0,1,1
+ .endm
.macro RESTORE_RSI_RDI
RESTORE_C_REGS_HELPER 0,0,0,0,0
.endm
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 4b3f3c1..4f113c8 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -756,9 +756,9 @@ retint_swapgs: /* return to user-space */
*/
irq_return_via_sysret:
CFI_REMEMBER_STATE
- RESTORE_C_REGS
- REMOVE_PT_GPREGS_FROM_STACK 8
- movq (RSP-RIP)(%rsp),%rsp
+ /* r11 is already restored (see code above) */
+ RESTORE_C_REGS_EXCEPT_R11
+ movq RSP(%rsp),%rsp
USERGS_SYSRET64
CFI_RESTORE_STATE
--
1.8.1.4
On Tue, Feb 24, 2015 at 4:30 PM, Denys Vlasenko <[email protected]> wrote:
> Avoid redundant load of %r11 (it is already loaded a few instructions before).
> Do not needlessly increment %rsp - we are going to return to userspace
> via SYSRET, this insn doesn't use stack for return.
Applied.
>
> Changes since v1: added a comment
>
> Signed-off-by: Denys Vlasenko <[email protected]>
> CC: Linus Torvalds <[email protected]>
> CC: Steven Rostedt <[email protected]>
> CC: Ingo Molnar <[email protected]>
> CC: Borislav Petkov <[email protected]>
> CC: "H. Peter Anvin" <[email protected]>
> CC: Andy Lutomirski <[email protected]>
> CC: Oleg Nesterov <[email protected]>
> CC: Frederic Weisbecker <[email protected]>
> CC: Alexei Starovoitov <[email protected]>
> CC: Will Drewry <[email protected]>
> CC: Kees Cook <[email protected]>
> CC: [email protected]
> CC: [email protected]
> ---
> arch/x86/include/asm/calling.h | 3 +++
> arch/x86/kernel/entry_64.S | 6 +++---
> 2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
> index 3374235..f1a962f 100644
> --- a/arch/x86/include/asm/calling.h
> +++ b/arch/x86/include/asm/calling.h
> @@ -176,6 +176,9 @@ For 32-bit we have the following conventions - kernel is built with
> .macro RESTORE_C_REGS_EXCEPT_RCX
> RESTORE_C_REGS_HELPER 1,0,1,1,1
> .endm
> + .macro RESTORE_C_REGS_EXCEPT_R11
> + RESTORE_C_REGS_HELPER 1,1,0,1,1
> + .endm
> .macro RESTORE_RSI_RDI
> RESTORE_C_REGS_HELPER 0,0,0,0,0
> .endm
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 4b3f3c1..4f113c8 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -756,9 +756,9 @@ retint_swapgs: /* return to user-space */
> */
> irq_return_via_sysret:
> CFI_REMEMBER_STATE
> - RESTORE_C_REGS
> - REMOVE_PT_GPREGS_FROM_STACK 8
> - movq (RSP-RIP)(%rsp),%rsp
> + /* r11 is already restored (see code above) */
> + RESTORE_C_REGS_EXCEPT_R11
> + movq RSP(%rsp),%rsp
> USERGS_SYSRET64
> CFI_RESTORE_STATE
>
> --
> 1.8.1.4
>
--
Andy Lutomirski
AMA Capital Management, LLC