linux-kernel - [PATCH V2 17/41] x86/entry: Make paranoid

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Message-Id: <20210926150838.197719-18-jiangshanlai@gmail.com>
Date:   Sun, 26 Sep 2021 23:08:14 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH V2 17/41] x86/entry: Make paranoid_exit() callable

From: Lai Jiangshan <laijs@...ux.alibaba.com>

Move the last JMP out of paranoid_exit() and make it callable.

Allow paranoid_exit() to be re-written in C later and also allow
asm_exc_nmi() to call it to avoid duplicated code.

No functional change intended.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 169ee14cc2d6..202253c9a4f2 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -443,7 +443,8 @@ SYM_CODE_START(\asmsym)
 
 	call	\cfunc
 
-	jmp	paranoid_exit
+	call	paranoid_exit
+	jmp	restore_regs_and_return_to_kernel
 
 	/* Switch to the regular task stack and use the noist entry point */
 .Lfrom_usermode_switch_stack_\@:
@@ -520,7 +521,8 @@ SYM_CODE_START(\asmsym)
 	 * identical to the stack in the IRET frame or the VC fall-back stack,
 	 * so it is definitely mapped even with PTI enabled.
 	 */
-	jmp	paranoid_exit
+	call	paranoid_exit
+	jmp	restore_regs_and_return_to_kernel
 
 	/* Switch to the regular task stack */
 .Lfrom_usermode_switch_stack_\@:
@@ -550,7 +552,8 @@ SYM_CODE_START(\asmsym)
 	movq	$-1, ORIG_RAX(%rsp)	/* no syscall to restart */
 	call	\cfunc
 
-	jmp	paranoid_exit
+	call	paranoid_exit
+	jmp	restore_regs_and_return_to_kernel
 
 _ASM_NOKPROBE(\asmsym)
 SYM_CODE_END(\asmsym)
@@ -937,7 +940,7 @@ SYM_CODE_END(paranoid_entry)
  *     Y        User space GSBASE, must be restored unconditionally
  */
 SYM_CODE_START_LOCAL(paranoid_exit)
-	UNWIND_HINT_REGS
+	UNWIND_HINT_REGS offset=8
 	/*
 	 * The order of operations is important. RESTORE_CR3 requires
 	 * kernel GSBASE.
@@ -953,16 +956,17 @@ SYM_CODE_START_LOCAL(paranoid_exit)
 
 	/* With FSGSBASE enabled, unconditionally restore GSBASE */
 	wrgsbase	%rbx
-	jmp		restore_regs_and_return_to_kernel
+	ret
 
 .Lparanoid_exit_checkgs:
 	/* On non-FSGSBASE systems, conditionally do SWAPGS */
 	testl		%ebx, %ebx
-	jnz		restore_regs_and_return_to_kernel
+	jnz		.Lparanoid_exit_done
 
 	/* We are returning to a context with user GSBASE */
 	swapgs
-	jmp		restore_regs_and_return_to_kernel
+.Lparanoid_exit_done:
+	ret
 SYM_CODE_END(paranoid_exit)
 
 SYM_CODE_START_LOCAL(error_return)
-- 
2.19.1.6.gb485710b