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Subject[PATCH V6 18/49] x86/entry: Switch the stack after error_entry() returns
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

error_entry() calls sync_regs() to settle/copy the pt_regs and switches
the stack directly after sync_regs(). But because error_entry() is also
called from entry, the switching has to handle the return address together,
which causes the behavior tangly.

Switching to the stack after error_entry() makes the code simpler and
intuitive.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry_64.S | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0d81f9b77367..e5d69604322d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -323,6 +323,8 @@ SYM_CODE_END(ret_from_fork)
.macro idtentry_body cfunc has_error_code:req

call error_entry
+ movq %rax, %rsp /* switch stack settled by sync_regs() */
+ ENCODE_FRAME_POINTER
UNWIND_HINT_REGS

movq %rsp, %rdi /* pt_regs pointer into 1st argument*/
@@ -985,14 +987,10 @@ SYM_CODE_START_LOCAL(error_entry)
/* We have user CR3. Change to kernel CR3. */
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax

+ leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */
.Lerror_entry_from_usermode_after_swapgs:
/* Put us onto the real thread stack. */
- popq %r12 /* save return addr in %12 */
- movq %rsp, %rdi /* arg0 = pt_regs pointer */
call sync_regs
- movq %rax, %rsp /* switch stack */
- ENCODE_FRAME_POINTER
- pushq %r12
ret

/*
@@ -1025,6 +1023,7 @@ SYM_CODE_START_LOCAL(error_entry)
*/
.Lerror_entry_done_lfence:
FENCE_SWAPGS_KERNEL_ENTRY
+ leaq 8(%rsp), %rax /* return pt_regs pointer */
ret

.Lbstep_iret:
@@ -1045,12 +1044,9 @@ SYM_CODE_START_LOCAL(error_entry)
* Pretend that the exception came from user mode: set up pt_regs
* as if we faulted immediately after IRET.
*/
- popq %r12 /* save return addr in %12 */
- movq %rsp, %rdi /* arg0 = pt_regs pointer */
+ leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */
call fixup_bad_iret
- mov %rax, %rsp
- ENCODE_FRAME_POINTER
- pushq %r12
+ mov %rax, %rdi
jmp .Lerror_entry_from_usermode_after_swapgs
SYM_CODE_END(error_entry)

--
2.19.1.6.gb485710b
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