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x86/uaccess: Move copy_user_handle_tail() into asm

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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
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@@ -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) \