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x86/asm/memcpy_mcsafe: Add write-protection-fault handling

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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: Tony Luck <tony.luck@intel.com>
Reported-by: Mika Penttilä <mika.penttila@nextfour.com>
Signed-off-by: Dan 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dan Williams 2018-05-03 17:06:26 -07:00 committed by Ingo Molnar
parent 60622d6822
commit 12c89130a5
3 changed files with 38 additions and 0 deletions
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3
arch/x86/include/asm/uaccess_64.h
View File

@ -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 */

14
arch/x86/lib/memcpy_64.S
View File

@ -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

21
arch/x86/lib/usercopy_64.c
View File

@ -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