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()

Author: torvalds

arch/x86/entry/calling.h

@@ -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

arch/x86/entry/entry_64.S

@@ -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