From 91aae953cb807d6fb7a70782b323bf9beb60d7c9 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 22 May 2021 22:48:36 +0300
Subject: [PATCH] amd64: clear PSL.AC in the right frame

If copyin family of routines fault, kernel does clear PSL.AC on the
fault entry, but the AC flag of the faulted frame is kept intact.  Since
onfault handler is effectively jump, AC survives until syscall exit.

Reported by:	m00nbsd, via Sony
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
admbugs:	975
---
 sys/amd64/amd64/support.S           | 18 ++++++++++++------
 sys/amd64/linux/linux_support.s     |  5 ++++-
 sys/amd64/linux32/linux32_support.s |  5 ++++-
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
index 0db6f2f04099..d511fe265996 100644
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -919,9 +919,11 @@ ENTRY(copyin_smap_erms)
 END(copyin_smap_erms)
 
 	ALIGN_TEXT
-	/* Trap entry clears PSL.AC */
 copy_fault:
-	movq	$0,PCB_ONFAULT(%r11)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r11)
 	movl	$EFAULT,%eax
 	POP_FRAME_POINTER
 	ret
@@ -1358,9 +1360,11 @@ ENTRY(subyte_smap)
 END(subyte_smap)
 
 	ALIGN_TEXT
-	/* Fault entry clears PSL.AC */
 fusufault:
-	movq	PCPU(CURPCB),%rcx
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	PCPU(CURPCB),%rcx
 	xorl	%eax,%eax
 	movq	%rax,PCB_ONFAULT(%rcx)
 	decq	%rax
@@ -1443,8 +1447,10 @@ ENTRY(copyinstr_smap)
 END(copyinstr_smap)
 
 cpystrflt:
-	/* Fault entry clears PSL.AC */
-	movl	$EFAULT,%eax
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movl	$EFAULT,%eax
 cpystrflt_x:
 	/* set *lencopied and return %eax */
 	movq	$0,PCB_ONFAULT(%r9)
diff --git a/sys/amd64/linux/linux_support.s b/sys/amd64/linux/linux_support.s
index 45eb565f667d..bb1c218bdf89 100644
--- a/sys/amd64/linux/linux_support.s
+++ b/sys/amd64/linux/linux_support.s
@@ -34,7 +34,10 @@
 #include "assym.inc"
 
 futex_fault:
-	movq	$0,PCB_ONFAULT(%r8)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r8)
 	movl	$-EFAULT,%eax
 	ret
 
diff --git a/sys/amd64/linux32/linux32_support.s b/sys/amd64/linux32/linux32_support.s
index da076010c13c..86f3d11b552b 100644
--- a/sys/amd64/linux32/linux32_support.s
+++ b/sys/amd64/linux32/linux32_support.s
@@ -34,7 +34,10 @@
 #include "assym.inc"
 
 futex_fault:
-	movq	$0,PCB_ONFAULT(%r8)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r8)
 	movl	$-EFAULT,%eax
 	ret