The following commit has been merged into the x86/entry branch of tip:
Commit-ID: 1e4d3001f59fb7a9917cb746544b65e616b5f809
Gitweb: https://git.kernel.org/tip/1e4d3001f59fb7a9917cb746544b65e616b5f809
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 20 Nov 2023 15:33:46 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 21 Nov 2023 13:57:31 +01:00
x86/entry: Harden return-to-user
Make the CONFIG_DEBUG_ENTRY=y check that validates CS is a user segment
unconditional and move it nearer to IRET.
PRE:
140,026,608 cycles:k ( +- 0.01% )
236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% )
POST:
139,957,681 cycles:k ( +- 0.01% )
236,681,819 instructions:k # 1.69 insn per cycle ( +- 0.00% )
(this is with --repeat 100 and the run-to-run variance is bigger than
the difference shown)
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231120143626.753200755@xxxxxxxxxxxxx
---
arch/x86/entry/entry_64.S | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index dfbf799..c40f89a 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -559,13 +559,6 @@ __irqentry_text_end:
SYM_CODE_START_LOCAL(common_interrupt_return)
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
IBRS_EXIT
-#ifdef CONFIG_DEBUG_ENTRY
- /* Assert that pt_regs indicates user mode. */
- testb $3, CS(%rsp)
- jnz 1f
- ud2
-1:
-#endif
#ifdef CONFIG_XEN_PV
ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
#endif
@@ -576,8 +569,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
STACKLEAK_ERASE
POP_REGS
add $8, %rsp /* orig_ax */
+ UNWIND_HINT_IRET_REGS
+
+.Lswapgs_and_iret:
swapgs
- jmp .Lnative_iret
+ /* Assert that the IRET frame indicates user mode. */
+ testb $3, 8(%rsp)
+ jnz .Lnative_iret
+ ud2
#ifdef CONFIG_PAGE_TABLE_ISOLATION
.Lpti_restore_regs_and_return_to_usermode:
@@ -613,8 +612,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
/* Restore RDI. */
popq %rdi
- swapgs
- jmp .Lnative_iret
+ jmp .Lswapgs_and_iret
#endif
SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
|