linux-kernel - [PATCH 5.15 03/78] x86/entry: Move PUSH_AND_CLEAR_REGS out of error

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Message-Id: <20220712183238.970721477@linuxfoundation.org>
Date:   Tue, 12 Jul 2022 20:38:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lai Jiangshan <jiangshan.ljs@...group.com>,
        Borislav Petkov <bp@...e.de>, Juergen Gross <jgross@...e.com>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: [PATCH 5.15 03/78] x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()

From: Lai Jiangshan <jiangshan.ljs@...group.com>

commit ee774dac0da1543376a69fd90840af6aa86879b3 upstream.

The macro idtentry() (through idtentry_body()) calls error_entry()
unconditionally even on XENPV. But XENPV needs to only push and clear
regs.

PUSH_AND_CLEAR_REGS in error_entry() makes the stack not return to its
original place when the function returns, which means it is not possible
to convert it to a C function.

Carve out PUSH_AND_CLEAR_REGS out of error_entry() and into a separate
function and call it before error_entry() in order to avoid calling
error_entry() on XENPV.

It will also allow for error_entry() to be converted to C code that can
use inlined sync_regs() and save a function call.

  [ bp: Massage commit message. ]

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Juergen Gross <jgross@...e.com>
Link: https://lore.kernel.org/r/20220503032107.680190-4-jiangshanlai@gmail.com
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/entry/entry_64.S |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -315,6 +315,14 @@ SYM_CODE_END(ret_from_fork)
 #endif
 .endm
 
+/* Save all registers in pt_regs */
+SYM_CODE_START_LOCAL(push_and_clear_regs)
+	UNWIND_HINT_FUNC
+	PUSH_AND_CLEAR_REGS save_ret=1
+	ENCODE_FRAME_POINTER 8
+	RET
+SYM_CODE_END(push_and_clear_regs)
+
 /**
  * idtentry_body - Macro to emit code calling the C function
  * @cfunc:		C function to be called
@@ -322,6 +330,9 @@ SYM_CODE_END(ret_from_fork)
  */
 .macro idtentry_body cfunc has_error_code:req
 
+	call push_and_clear_regs
+	UNWIND_HINT_REGS
+
 	call	error_entry
 	movq	%rax, %rsp			/* switch to the task stack if from userspace */
 	ENCODE_FRAME_POINTER
@@ -965,13 +976,11 @@ SYM_CODE_START_LOCAL(paranoid_exit)
 SYM_CODE_END(paranoid_exit)
 
 /*
- * Save all registers in pt_regs, and switch GS if needed.
+ * Switch GS and CR3 if needed.
  */
 SYM_CODE_START_LOCAL(error_entry)
 	UNWIND_HINT_FUNC
 	cld
-	PUSH_AND_CLEAR_REGS save_ret=1
-	ENCODE_FRAME_POINTER 8
 	testb	$3, CS+8(%rsp)
 	jz	.Lerror_kernelspace