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x86/uaccess: Move copy_user_handle_tail() into asm 

By writing the function in asm we avoid cross object code flow and
objtool no longer gets confused about a 'stray' CLAC.

Also; the asm version is actually _simpler_.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-03-01 15:24:33 +01:00 committed by Ingo Molnar
parent 8f4faed01e
commit 3693ca8115
4 changed files with 48 additions and 47 deletions
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24
arch/x86/include/asm/asm.h
View File

@ -148,30 +148,6 @@
_ASM_PTR (entry); \
.popsection
.macro ALIGN_DESTINATION
/* check for bad alignment of destination */
movl %edi,%ecx
andl $7,%ecx
jz 102f /* already aligned */
subl $8,%ecx
negl %ecx
subl %ecx,%edx
100: movb (%rsi),%al
101: movb %al,(%rdi)
incq %rsi
incq %rdi
decl %ecx
jnz 100b
102:
.section .fixup,"ax"
103: addl %ecx,%edx /* ecx is zerorest also */
jmp copy_user_handle_tail
.previous
_ASM_EXTABLE_UA(100b, 103b)
_ASM_EXTABLE_UA(101b, 103b)
.endm
#else
# define _EXPAND_EXTABLE_HANDLE(x) #x
# define _ASM_EXTABLE_HANDLE(from, to, handler) \

3
arch/x86/include/asm/uaccess_64.h
View File

@ -207,9 +207,6 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size)
return __copy_user_flushcache(dst, src, size);
}
unsigned long
copy_user_handle_tail(char *to, char *from, unsigned len);
unsigned long
mcsafe_handle_tail(char *to, char *from, unsigned len);

48
arch/x86/lib/copy_user_64.S
View File

@ -16,6 +16,30 @@
#include <asm/smap.h>
#include <asm/export.h>
.macro ALIGN_DESTINATION
/* check for bad alignment of destination */
movl %edi,%ecx
andl $7,%ecx
jz 102f /* already aligned */
subl $8,%ecx
negl %ecx
subl %ecx,%edx
100: movb (%rsi),%al
101: movb %al,(%rdi)
incq %rsi
incq %rdi
decl %ecx
jnz 100b
102:
.section .fixup,"ax"
103: addl %ecx,%edx /* ecx is zerorest also */
jmp copy_user_handle_tail
.previous
_ASM_EXTABLE_UA(100b, 103b)
_ASM_EXTABLE_UA(101b, 103b)
.endm
/*
* copy_user_generic_unrolled - memory copy with exception handling.
* This version is for CPUs like P4 that don't have efficient micro
@ -193,6 +217,30 @@ ENTRY(copy_user_enhanced_fast_string)
ENDPROC(copy_user_enhanced_fast_string)
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.
*
* Input:
* rdi destination
* rsi source
* rdx count
*
* Output:
* eax uncopied bytes or 0 if successful.
*/
ALIGN;
copy_user_handle_tail:
movl %edx,%ecx
1: rep movsb
2: mov %ecx,%eax
ASM_CLAC
ret
_ASM_EXTABLE_UA(1b, 2b)
ENDPROC(copy_user_handle_tail)
/*
* copy_user_nocache - Uncached memory copy with exception handling
* This will force destination out of cache for more performance.

20
arch/x86/lib/usercopy_64.c
View File

@ -54,26 +54,6 @@ unsigned long clear_user(void __user *to, unsigned long n)
}
EXPORT_SYMBOL(clear_user);
/*
* 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.
*/
__visible unsigned long
copy_user_handle_tail(char *to, char *from, unsigned len)
{
for (; len; --len, to++) {
char c;
if (__get_user_nocheck(c, from++, sizeof(char)))
break;
if (__put_user_nocheck(c, to, sizeof(char)))
break;
}
clac();
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.