x86/asm/memcpy_mcsafe: Add write-protection-fault handling (12c89130) · Commits · 戴 / test

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>

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

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