linux-kernel - [tip: x86/asm] x86/traps: Use pt_regs directly in fixup_bad

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Date:   Tue, 03 May 2022 19:01:07 -0000
From:   "tip-bot2 for Lai Jiangshan" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Lai Jiangshan <jiangshan.ljs@...group.com>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/traps: Use pt_regs directly in fixup_bad_iret()

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     0aca53c6b522f8d6e2681ca875acbbe105f5fdcf
Gitweb:        https://git.kernel.org/tip/0aca53c6b522f8d6e2681ca875acbbe105f5fdcf
Author:        Lai Jiangshan <jiangshan.ljs@...group.com>
AuthorDate:    Thu, 21 Apr 2022 22:10:48 +08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Tue, 03 May 2022 11:18:59 +02:00

x86/traps: Use pt_regs directly in fixup_bad_iret()

Always stash the address error_entry() is going to return to, in %r12
and get rid of the void *error_entry_ret; slot in struct bad_iret_stack
which was supposed to account for it and pt_regs pushed on the stack.

After this, both fixup_bad_iret() and sync_regs() can work on a struct
pt_regs pointer directly.

  [ bp: Rewrite commit message, touch ups. ]

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lore.kernel.org/r/20220503032107.680190-2-jiangshanlai@gmail.com
---
 arch/x86/entry/entry_64.S    |  5 ++++-
 arch/x86/include/asm/traps.h |  2 +-
 arch/x86/kernel/traps.c      | 19 +++++++------------
 3 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 73d9585..ecbfca3 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1061,9 +1061,12 @@ 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.
 	 */
-	mov	%rsp, %rdi
+	popq	%r12				/* save return addr in %12 */
+	movq	%rsp, %rdi			/* arg0 = pt_regs pointer */
 	call	fixup_bad_iret
 	mov	%rax, %rsp
+	ENCODE_FRAME_POINTER
+	pushq	%r12
 	jmp	.Lerror_entry_from_usermode_after_swapgs
 SYM_CODE_END(error_entry)
 
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 35317c5..47ecfff 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -13,7 +13,7 @@
 #ifdef CONFIG_X86_64
 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs);
 asmlinkage __visible notrace
-struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s);
+struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs);
 void __init trap_init(void);
 asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *eregs);
 #endif
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 1563fb9..4167215 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -892,14 +892,10 @@ sync:
 }
 #endif
 
-struct bad_iret_stack {
-	void *error_entry_ret;
-	struct pt_regs regs;
-};
-
-asmlinkage __visible noinstr
-struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
+asmlinkage __visible noinstr struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs)
 {
+	struct pt_regs tmp, *new_stack;
+
 	/*
 	 * This is called from entry_64.S early in handling a fault
 	 * caused by a bad iret to user mode.  To handle the fault
@@ -908,19 +904,18 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 	 * just below the IRET frame) and we want to pretend that the
 	 * exception came from the IRET target.
 	 */
-	struct bad_iret_stack tmp, *new_stack =
-		(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+	new_stack = (struct pt_regs *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
 	/* Copy the IRET target to the temporary storage. */
-	__memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
+	__memcpy(&tmp.ip, (void *)bad_regs->sp, 5*8);
 
 	/* Copy the remainder of the stack from the current stack. */
-	__memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+	__memcpy(&tmp, bad_regs, offsetof(struct pt_regs, ip));
 
 	/* Update the entry stack */
 	__memcpy(new_stack, &tmp, sizeof(tmp));
 
-	BUG_ON(!user_mode(&new_stack->regs));
+	BUG_ON(!user_mode(new_stack));
 	return new_stack;
 }
 #endif