2023-04-03 14:11:46

by Lai Jiangshan

Subject: [RFC PATCH 1/7] x86/entry: Move PUSH_AND_CLEAR_REGS out of paranoid_entry

From: Lai Jiangshan <[email protected]>

Prepare to call paranoid_entry() with pt_regs pushed.

Signed-off-by: Lai Jiangshan <[email protected]>
---
arch/x86/entry/entry_64.S | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index eccc3431e515..49ddc4dd3117 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -475,11 +475,13 @@ SYM_CODE_START(\asmsym)
testb $3, CS-ORIG_RAX(%rsp)
jnz .Lfrom_usermode_switch_stack_\@

+ PUSH_AND_CLEAR_REGS
+ UNWIND_HINT_REGS
+ ENCODE_FRAME_POINTER
+
/* paranoid_entry returns GS information for paranoid_exit in EBX. */
call paranoid_entry

- UNWIND_HINT_REGS
-
movq %rsp, %rdi /* pt_regs pointer */

call \cfunc
@@ -530,14 +532,16 @@ SYM_CODE_START(\asmsym)
testb $3, CS-ORIG_RAX(%rsp)
jnz .Lfrom_usermode_switch_stack_\@

+ PUSH_AND_CLEAR_REGS
+ UNWIND_HINT_REGS
+ ENCODE_FRAME_POINTER
+
/*
* paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
* EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
*/
call paranoid_entry

- UNWIND_HINT_REGS
-
/*
* Switch off the IST stack to make it free for nested exceptions. The
* vc_switch_off_ist() function will switch back to the interrupted
@@ -587,9 +591,12 @@ SYM_CODE_START(\asmsym)
ASM_CLAC
cld

+ PUSH_AND_CLEAR_REGS
+ UNWIND_HINT_REGS
+ ENCODE_FRAME_POINTER
+
/* paranoid_entry returns GS information for paranoid_exit in EBX. */
call paranoid_entry
- UNWIND_HINT_REGS

movq %rsp, %rdi /* pt_regs pointer into first argument */
movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/
@@ -903,8 +910,8 @@ SYM_CODE_END(xen_failsafe_callback)
#endif /* CONFIG_XEN_PV */

/*
- * Save all registers in pt_regs. Return GSBASE related information
- * in EBX depending on the availability of the FSGSBASE instructions:
+ * Return GSBASE related information in EBX depending on the availability
+ * of the FSGSBASE instructions:
*
* FSGSBASE R/EBX
* N 0 -> SWAPGS on exit
@@ -915,11 +922,8 @@ SYM_CODE_END(xen_failsafe_callback)
* R14 - old CR3
* R15 - old SPEC_CTRL
*/
-SYM_CODE_START(paranoid_entry)
+SYM_FUNC_START(paranoid_entry)
ANNOTATE_NOENDBR
- UNWIND_HINT_FUNC
- PUSH_AND_CLEAR_REGS save_ret=1
- ENCODE_FRAME_POINTER 8

/*
* Always stash CR3 in %r14. This value will be restored,
@@ -988,7 +992,7 @@ SYM_CODE_START(paranoid_entry)
UNTRAIN_RET_FROM_CALL

RET
-SYM_CODE_END(paranoid_entry)
+SYM_FUNC_END(paranoid_entry)

/*
* "Paranoid" exit path from exception stack. This is invoked
@@ -1443,6 +1447,10 @@ end_repeat_nmi:
*/
pushq $-1 /* ORIG_RAX: no syscall to restart */

+ PUSH_AND_CLEAR_REGS
+ UNWIND_HINT_REGS
+ ENCODE_FRAME_POINTER
+
/*
* Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit
* as we should not be calling schedule in NMI context.
@@ -1451,7 +1459,6 @@ end_repeat_nmi:
* exceptions might do.
*/
call paranoid_entry
- UNWIND_HINT_REGS

movq %rsp, %rdi
movq $-1, %rsi
--
2.19.1.6.gb485710b

2023-04-06 20:42:53

by Peter Zijlstra

Subject: Re: [RFC PATCH 1/7] x86/entry: Move PUSH_AND_CLEAR_REGS out of paranoid_entry

On Mon, Apr 03, 2023 at 10:05:59PM +0800, Lai Jiangshan wrote:
> @@ -915,11 +922,8 @@ SYM_CODE_END(xen_failsafe_callback)
> * R14 - old CR3
> * R15 - old SPEC_CTRL
> */
> -SYM_CODE_START(paranoid_entry)
> +SYM_FUNC_START(paranoid_entry)
> ANNOTATE_NOENDBR
> - UNWIND_HINT_FUNC

That isn't quite equivalent. SYM_FUNC_START() gets you ENDBR, while the
SYM_CODE_START(); ANNOTATE_NOENDBR; UNWIND_HINT_FUNC is
explicitly no ENDBR.


> - PUSH_AND_CLEAR_REGS save_ret=1
> - ENCODE_FRAME_POINTER 8
>
> /*
> * Always stash CR3 in %r14. This value will be restored,