linux-kernel - [PATCH 1/4] x86/mce: Fix copyin code to return -EFAULT on machine check.

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Date:   Thu, 25 Mar 2021 17:02:32 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andy Lutomirski <luto@...nel.org>,
        Aili Yao <yaoaili@...gsoft.com>,
        HORIGUCHI NAOYA( 堀口　直也) 
        <naoya.horiguchi@....com>
Subject: [PATCH 1/4] x86/mce: Fix copyin code to return -EFAULT on machine check.

When copy from user fails due to a machine check on poison reading
user data it should return an error code.

---

Separate patch just now, but likely needs to be combined with patches
to iteration code for bisection safety.
---
 arch/x86/lib/copy_user_64.S | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 77b9b2a3b5c8..2987118c541a 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -14,6 +14,7 @@
 #include <asm/alternative-asm.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/errno.h>
 #include <asm/export.h>
 #include <asm/trapnr.h>
 
@@ -237,18 +238,21 @@ SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
 	cmp $X86_TRAP_MC,%eax		/* check if X86_TRAP_MC */
 	je 3f
 1:	rep movsb
-2:	mov %ecx,%eax
+	mov %ecx,%eax
+	ASM_CLAC
+	ret
+
+2:
+	cmp $X86_TRAP_MC,%eax
+	je 3f
+	mov %ecx,%eax
 	ASM_CLAC
 	ret
 
 	/*
-	 * Return zero to pretend that this copy succeeded. This
-	 * is counter-intuitive, but needed to prevent the code
-	 * in lib/iov_iter.c from retrying and running back into
-	 * the poison cache line again. The machine check handler
-	 * will ensure that a SIGBUS is sent to the task.
+	 * Return -EFAULT for the machine check cases
 	 */
-3:	xorl %eax,%eax
+3:	movl $-EFAULT,%eax
 	ASM_CLAC
 	ret
 
-- 
2.29.2