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x86/entry: Switch the stack after error_entry() returns 

error_entry() calls fixup_bad_iret() before sync_regs() if it is a fault
from a bad IRET, to copy pt_regs to the kernel stack. It switches to the
kernel stack directly after sync_regs().

But error_entry() itself is also a function call, so it has to stash
the address it is going to return to, in %r12 which is unnecessarily
complicated.

Move the stack switching after error_entry() and get rid of the need to
handle the return address.

  [ bp: Massage commit message. ]

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220503032107.680190-3-jiangshanlai@gmail.com
This commit is contained in:
Lai Jiangshan 2022-04-21 22:10:49 +08:00 committed by Borislav Petkov
parent 0aca53c6b5
commit 520a7e80c9
1 changed files with 6 additions and 10 deletions
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16
arch/x86/entry/entry_64.S
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@ -326,6 +326,8 @@ SYM_CODE_END(ret_from_fork)
.macro idtentry_body cfunc has_error_code:req
call error_entry
movq %rax, %rsp /* switch to the task stack if from userspace */
ENCODE_FRAME_POINTER
UNWIND_HINT_REGS
movq %rsp, %rdi /* pt_regs pointer into 1st argument*/
@ -1002,14 +1004,10 @@ 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
/*
@ -1041,6 +1039,7 @@ 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:
@ -1061,12 +1060,9 @@ 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)