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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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20
arch/x86/lib/usercopy_64.c
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@@ -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.