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parisc: Clean up fixup routines for get_user()/put_user()

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Al Viro noticed that userspace accesses via get_user()/put_user() can be
simplified a lot with regard to usage of the exception handling.

This patch implements a fixup routine for get_user() and put_user() in such
that the exception handler will automatically load -EFAULT into the register
%r8 (the error value) in case on a fault on userspace.  Additionally the fixup
routine will zero the target register on fault in case of a get_user() call.
The target register is extracted out of the faulting assembly instruction.

This patch brings a few benefits over the old implementation:
1. Exception handling gets much cleaner, easier and smaller in size.
2. Helper functions like fixup_get_user_skip_1 (all of fixup.S) can be dropped.
3. No need to hardcode %r9 as target register for get_user() any longer. This
   helps the compiler register allocator and thus creates less assembler
   statements.
4. No dependency on the exception_data contents any longer.
5. Nested faults will be handled cleanly.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Helge Deller
2017-03-25 11:59:15 +01:00
parent 554bfeceb8
commit d19f5e41b3
5 changed files with 52 additions and 134 deletions
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10
arch/parisc/kernel/parisc_ksyms.c
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@@ -47,16 +47,6 @@ EXPORT_SYMBOL(__cmpxchg_u64);
EXPORT_SYMBOL(lclear_user);
EXPORT_SYMBOL(lstrnlen_user);
/* Global fixups - defined as int to avoid creation of function pointers */
extern int fixup_get_user_skip_1;
extern int fixup_get_user_skip_2;
extern int fixup_put_user_skip_1;
extern int fixup_put_user_skip_2;
EXPORT_SYMBOL(fixup_get_user_skip_1);
EXPORT_SYMBOL(fixup_get_user_skip_2);
EXPORT_SYMBOL(fixup_put_user_skip_1);
EXPORT_SYMBOL(fixup_put_user_skip_2);
#ifndef CONFIG_64BIT
/* Needed so insmod can set dp value */
extern int $global$;