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Commit 12c89130 authored by Dan Williams's avatar Dan Williams Committed by Ingo Molnar
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x86/asm/memcpy_mcsafe: Add write-protection-fault handling 



In preparation for using memcpy_mcsafe() to handle user copies it needs
to be to handle write-protection faults while writing user pages. Add
MMU-fault handlers alongside the machine-check exception handlers.

Note that the machine check fault exception handling makes assumptions
about source buffer alignment and poison alignment. In the write fault
case, given the destination buffer is arbitrarily aligned, it needs a
separate / additional fault handling approach. The mcsafe_handle_tail()
helper is reused. The @limit argument is set to @len since there is no
safety concern about retriggering an MMU fault, and this simplifies the
assembly.

Co-developed-by: default avatarTony Luck <tony.luck@intel.com>
Reported-by: default avatarMika Penttilä <mika.penttila@nextfour.com>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: hch@lst.de
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-nvdimm@lists.01.org
Link: http://lkml.kernel.org/r/152539238635.31796.14056325365122961778.stgit@dwillia2-desk3.amr.corp.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 60622d68

arch/x86/include/asm/uaccess_64.h

+3 −0
Original line number Diff line number Diff line
@@ -194,4 +194,7 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size) 
unsigned long

copy_user_handle_tail(char *to, char *from, unsigned len);



unsigned long

mcsafe_handle_tail(char *to, char *from, unsigned len);



#endif /* _ASM_X86_UACCESS_64_H */

arch/x86/lib/memcpy_64.S

+14 −0
Original line number Diff line number Diff line
@@ -265,9 +265,23 @@ EXPORT_SYMBOL_GPL(__memcpy_mcsafe) 
	mov	%ecx, %eax

	ret



	/*

	 * For write fault handling, given the destination is unaligned,

	 * we handle faults on multi-byte writes with a byte-by-byte

	 * copy up to the write-protected page.

	 */

.E_write_words:

	shll	$3, %ecx

	addl	%edx, %ecx

	movl	%ecx, %edx

	jmp mcsafe_handle_tail



	.previous



	_ASM_EXTABLE_FAULT(.L_read_leading_bytes, .E_leading_bytes)

	_ASM_EXTABLE_FAULT(.L_read_words, .E_read_words)

	_ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .E_trailing_bytes)

	_ASM_EXTABLE(.L_write_leading_bytes, .E_leading_bytes)

	_ASM_EXTABLE(.L_write_words, .E_write_words)

	_ASM_EXTABLE(.L_write_trailing_bytes, .E_trailing_bytes)

#endif

arch/x86/lib/usercopy_64.c

+21 −0
Original line number Diff line number Diff line
@@ -75,6 +75,27 @@ copy_user_handle_tail(char *to, char *from, unsigned len) 
	return len;

}



/*

 * Similar to copy_user_handle_tail, probe for the write fault point,

 * but reuse __memcpy_mcsafe in case a new read error is encountered.

 * clac() is handled in _copy_to_iter_mcsafe().

 */

__visible unsigned long

mcsafe_handle_tail(char *to, char *from, unsigned len)

{

	for (; len; --len, to++, from++) {

		/*

		 * Call the assembly routine back directly since

		 * memcpy_mcsafe() may silently fallback to memcpy.

		 */

		unsigned long rem = __memcpy_mcsafe(to, from, 1);



		if (rem)

			break;

	}

	return len;

}



#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE

/**

 * clean_cache_range - write back a cache range with CLWB