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Date: Wed, 31 Jan 2024 21:14:42 -0000
From: "tip-bot2 for Peter Zijlstra (Intel)" <tip-bot2@linutronix.de>
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Subject: [tip: x86/fred] x86/entry/calling: Allow PUSH_AND_CLEAR_REGS being
 used beyond actual entry code
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
 Xin Li <xin3.li@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
 "Borislav Petkov (AMD)" <bp@alien8.de>, Shan Kang <shan.kang@intel.com>,
 x86@kernel.org, linux-kernel@vger.kernel.org
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The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     2333f3c473c1562633cd17ac2eb743c29c3b2d9d
Gitweb:        https://git.kernel.org/tip/2333f3c473c1562633cd17ac2eb743c29c3b2d9d
Author:        Peter Zijlstra (Intel) <peterz@infradead.org>
AuthorDate:    Tue, 05 Dec 2023 02:50:19 -08:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 31 Jan 2024 22:03:09 +01:00

x86/entry/calling: Allow PUSH_AND_CLEAR_REGS being used beyond actual entry code

PUSH_AND_CLEAR_REGS could be used besides actual entry code; in that case
%rbp shouldn't be cleared (otherwise the frame pointer is destroyed) and
UNWIND_HINT shouldn't be added.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-31-xin3.li@intel.com
---
 arch/x86/entry/calling.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 9f1d947..3ff925b 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -65,7 +65,7 @@ For 32-bit we have the following conventions - kernel is built with
  * for assembly code:
  */
 
-.macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0
+.macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 unwind_hint=1
 	.if \save_ret
 	pushq	%rsi		/* pt_regs->si */
 	movq	8(%rsp), %rsi	/* temporarily store the return address in %rsi */
@@ -87,14 +87,17 @@ For 32-bit we have the following conventions - kernel is built with
 	pushq	%r13		/* pt_regs->r13 */
 	pushq	%r14		/* pt_regs->r14 */
 	pushq	%r15		/* pt_regs->r15 */
+
+	.if \unwind_hint
 	UNWIND_HINT_REGS
+	.endif
 
 	.if \save_ret
 	pushq	%rsi		/* return address on top of stack */
 	.endif
 .endm
 
-.macro CLEAR_REGS
+.macro CLEAR_REGS clear_bp=1
 	/*
 	 * Sanitize registers of values that a speculation attack might
 	 * otherwise want to exploit. The lower registers are likely clobbered
@@ -109,7 +112,9 @@ For 32-bit we have the following conventions - kernel is built with
 	xorl	%r10d, %r10d	/* nospec r10 */
 	xorl	%r11d, %r11d	/* nospec r11 */
 	xorl	%ebx,  %ebx	/* nospec rbx */
+	.if \clear_bp
 	xorl	%ebp,  %ebp	/* nospec rbp */
+	.endif
 	xorl	%r12d, %r12d	/* nospec r12 */
 	xorl	%r13d, %r13d	/* nospec r13 */
 	xorl	%r14d, %r14d	/* nospec r14 */
@@ -117,9 +122,9 @@ For 32-bit we have the following conventions - kernel is built with
 
 .endm
 
-.macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0
-	PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret
-	CLEAR_REGS
+.macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 clear_bp=1 unwind_hint=1
+	PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret unwind_hint=\unwind_hint
+	CLEAR_REGS clear_bp=\clear_bp
 .endm
 
 .macro POP_REGS pop_rdi=1