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x86/uaccess: Don't leak AC flag into fentry from mcsafe_handle_tail() 

After adding mcsafe_handle_tail() to the objtool uaccess safe list,
objtool reports:

  arch/x86/lib/usercopy_64.o: warning: objtool: mcsafe_handle_tail()+0x0: call to __fentry__() with UACCESS enabled

With SMAP, this function is called with AC=1, so it needs to be careful
about which functions it calls.  Disable the ftrace entry hook, which
can potentially pull in a lot of extra code.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/8e13d6f0da1c8a3f7603903da6cbf6d582bbfe10.1563413318.git.jpoimboe@redhat.com
This commit is contained in:
Josh Poimboeuf 2019-07-17 20:36:43 -05:00 committed by Thomas Gleixner
parent 3a6ab4bcc5
commit 5e307a6bc7
1 changed files with 1 additions and 1 deletions
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arch/x86/lib/usercopy_64.c
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@ -60,7 +60,7 @@ EXPORT_SYMBOL(clear_user);
* but reuse __memcpy_mcsafe in case a new read error is encountered.
* clac() is handled in _copy_to_iter_mcsafe().
*/
__visible unsigned long
__visible notrace unsigned long
mcsafe_handle_tail(char *to, char *from, unsigned len)
{
for (; len; --len, to++, from++) {