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From: Tony Luck <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>,
	Youquan Song <youquan.song@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v3 4/6] x86/mce: Avoid tail copy when machine check terminated a copy from user
Date: Tue,  6 Oct 2020 14:09:08 -0700	[thread overview]
Message-ID: <20201006210910.21062-5-tony.luck@intel.com> (raw)
In-Reply-To: <20201006210910.21062-1-tony.luck@intel.com>

In the page fault case it is ok to see if a few more unaligned bytes
can be copied from the source address. Worst case is that the page fault
will be triggered again.

Machine checks are more serious. Just give up at the point where the
main copy loop triggered the #MC and return from the copy code as if
the copy succeeded. The machine check handler will use task_work_add() to
make sure that the task is sent a SIGBUS.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/lib/copy_user_64.S | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 5b68e945bf65..77b9b2a3b5c8 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -15,6 +15,7 @@
 #include <asm/asm.h>
 #include <asm/smap.h>
 #include <asm/export.h>
+#include <asm/trapnr.h>
 
 .macro ALIGN_DESTINATION
 	/* check for bad alignment of destination */
@@ -221,6 +222,7 @@ EXPORT_SYMBOL(copy_user_enhanced_fast_string)
  * Try to copy last bytes and clear the rest if needed.
  * Since protection fault in copy_from/to_user is not a normal situation,
  * it is not necessary to optimize tail handling.
+ * Don't try to copy the tail if machine check happened
  *
  * Input:
  * rdi destination
@@ -232,11 +234,24 @@ EXPORT_SYMBOL(copy_user_enhanced_fast_string)
  */
 SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
 	movl %edx,%ecx
+	cmp $X86_TRAP_MC,%eax		/* check if X86_TRAP_MC */
+	je 3f
 1:	rep movsb
 2:	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.
+	 */
+3:	xorl %eax,%eax
+	ASM_CLAC
+	ret
+
 	_ASM_EXTABLE_CPY(1b, 2b)
 SYM_CODE_END(.Lcopy_user_handle_tail)
 
-- 
2.21.1


  parent reply	other threads:[~2020-10-06 21:09 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200908175519.14223-1-tony.luck@intel.com>
2020-09-08 17:55 ` [PATCH 1/8] x86/mce: Stop mce_reign() from re-computing severity for every CPU Tony Luck
2020-09-14 17:21   ` Borislav Petkov
2020-09-14 17:32   ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-09-08 17:55 ` [PATCH 4/8] x86/mce: Add _ASM_EXTABLE_CPY for copy user access Tony Luck
2020-09-16  9:59   ` Borislav Petkov
2020-09-08 17:55 ` [PATCH 5/8] x86/mce: Avoid tail copy when machine check terminated a copy from user Tony Luck
2020-09-16 10:53   ` Borislav Petkov
2020-09-16 19:26     ` Luck, Tony
2020-09-17 17:04       ` Borislav Petkov
2020-09-17 21:57         ` Luck, Tony
2020-09-18  7:51           ` Borislav Petkov
2020-09-08 17:55 ` [PATCH 6/8] x86/mce: Change fault_in_kernel_space() from static to global Tony Luck
2020-09-08 17:55 ` [PATCH 7/8] x86/mce: Recover from poison found while copying from user space Tony Luck
2020-09-18 16:13   ` Borislav Petkov
2020-09-08 17:55 ` [PATCH 8/8] x86/mce: Decode a kernel instruction to determine if it is copying from user Tony Luck
2020-09-21 11:31   ` Borislav Petkov
2020-09-30 23:26     ` [PATCH v2 0/7] Add machine check recovery when copying from user space Tony Luck
2020-09-30 23:26       ` [PATCH v2 1/7] x86/mce: Pass pointer to saved pt_regs to severity calculation routines Tony Luck
2020-09-30 23:26       ` [PATCH v2 2/7] x86/mce: Provide method to find out the type of exception handle Tony Luck
2020-10-05 16:35         ` Borislav Petkov
2020-09-30 23:26       ` [PATCH v2 3/7] x86/mce: Add _ASM_EXTABLE_CPY for copy user access Tony Luck
2020-10-05 16:34         ` Borislav Petkov
2020-09-30 23:26       ` [PATCH v2 4/7] x86/mce: Avoid tail copy when machine check terminated a copy from user Tony Luck
2020-09-30 23:26       ` [PATCH v2 5/7] x86/mce: Change fault_in_kernel_space() from static to global Tony Luck
2020-10-05 16:33         ` Borislav Petkov
2020-09-30 23:26       ` [PATCH v2 6/7] x86/mce: Recover from poison found while copying from user space Tony Luck
2020-10-05 16:32         ` Borislav Petkov
2020-10-05 17:47           ` Luck, Tony
2020-09-30 23:26       ` [PATCH v2 7/7] x86/mce: Decode a kernel instruction to determine if it is copying from user Tony Luck
2020-10-05 16:31         ` Borislav Petkov
2020-10-06 21:09           ` [PATCH v3 0/6] Add machine check recovery when copying from user space Tony Luck
2020-10-06 21:09             ` [PATCH v3 1/6] x86/mce: Pass pointer to saved pt_regs to severity calculation routines Tony Luck
2020-10-07 10:02               ` [tip: ras/core] " tip-bot2 for Youquan Song
2020-10-06 21:09             ` [PATCH v3 2/6] x86/mce: Provide method to find out the type of exception handle Tony Luck
2020-10-07 10:02               ` [tip: ras/core] x86/mce: Provide method to find out the type of an exception handler tip-bot2 for Tony Luck
2020-10-06 21:09             ` [PATCH v3 3/6] x86/mce: Add _ASM_EXTABLE_CPY for copy user access Tony Luck
2020-10-07 10:02               ` [tip: ras/core] " tip-bot2 for Youquan Song
2020-10-06 21:09             ` Tony Luck [this message]
2020-10-07  8:23               ` [PATCH v3 4/6] x86/mce: Avoid tail copy when machine check terminated a copy from user David Laight
2020-10-07 18:49                 ` Luck, Tony
2020-10-07 21:11                   ` David Laight
2020-10-07 10:02               ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-10-06 21:09             ` [PATCH v3 5/6] x86/mce: Recover from poison found while copying from user space Tony Luck
2020-10-07 10:02               ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-10-06 21:09             ` [PATCH v3 6/6] x86/mce: Decode a kernel instruction to determine if it is copying from user Tony Luck
2020-10-07 10:02               ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-09-09 15:05 ` [RESEND PATCH 0/8] Add machine check recovery when copying from user space Tony Luck
     [not found] ` <20200908175519.14223-4-tony.luck@intel.com>
2020-09-15  9:11   ` [PATCH 3/8] x86/mce: Provide method to find out the type of exception handle Borislav Petkov
2020-09-15 16:24     ` Luck, Tony

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