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x86/entry changes for v6.8:

Browse Source 
- Optimize common_interrupt_return()
 
  - Harden the return-to-user code by making a CONFIG_DEBUG_ENTRY=y
    check unconditional & moving it closer to the IRET.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'x86-entry-2024-01-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 entry updates from Ingo Molnar:

 - Optimize common_interrupt_return()

 - Harden the return-to-user code by making a CONFIG_DEBUG_ENTRY=y check
   unconditional & moving it closer to the IRET.

* tag 'x86-entry-2024-01-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/entry: Harden return-to-user
  x86/entry: Optimize common_interrupt_return()
This commit is contained in:
Linus Torvalds 2024-01-08 17:48:35 -08:00
commit 2fdbcf715a
2 changed files with 31 additions and 14 deletions
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12
arch/x86/entry/calling.h
View File

@ -175,8 +175,7 @@ For 32-bit we have the following conventions - kernel is built with
#define THIS_CPU_user_pcid_flush_mask \
PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask
.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
.macro SWITCH_TO_USER_CR3 scratch_reg:req scratch_reg2:req
mov %cr3, \scratch_reg
ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
@ -206,13 +205,20 @@ For 32-bit we have the following conventions - kernel is built with
/* Flip the PGD to the user version */
orq $(PTI_USER_PGTABLE_MASK), \scratch_reg
mov \scratch_reg, %cr3
.endm
.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
SWITCH_TO_USER_CR3 \scratch_reg \scratch_reg2
.Lend_\@:
.endm
.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
pushq %rax
SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax
SWITCH_TO_USER_CR3 scratch_reg=\scratch_reg scratch_reg2=%rax
popq %rax
.Lend_\@:
.endm
.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req

33
arch/x86/entry/entry_64.S
View File

@ -559,17 +559,27 @@ __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
#ifdef CONFIG_PAGE_TABLE_ISOLATION
ALTERNATIVE "", "jmp .Lpti_restore_regs_and_return_to_usermode", X86_FEATURE_PTI
#endif
STACKLEAK_ERASE
POP_REGS
add $8, %rsp /* orig_ax */
UNWIND_HINT_IRET_REGS
.Lswapgs_and_iret:
swapgs
/* 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:
POP_REGS pop_rdi=0
/*
@ -596,13 +606,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
*/
STACKLEAK_ERASE_NOCLOBBER
SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
push %rax
SWITCH_TO_USER_CR3 scratch_reg=%rdi scratch_reg2=%rax
pop %rax
/* 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)
#ifdef CONFIG_DEBUG_ENTRY