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futex: fix user access on powerpc

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The powerpc user access code is special, and unlike other architectures
distinguishes between user access for reading and writing.

And commit 43a43faf53 ("futex: improve user space accesses") messed
that up.  It went undetected elsewhere, but caused ppc32 to fail early
during boot, because the user access had been started with
user_read_access_begin(), but then finished off with just a plain
"user_access_end()".

Note that the address-masking user access helpers don't even have that
read-vs-write distinction, so if powerpc ever wants to do address
masking tricks, we'll have to do some extra work for it.

[ Make sure to also do it for the EFAULT case, as pointed out by
  Christophe Leroy ]

Reported-by: Andreas Schwab <schwab@linux-m68k.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/all/87bjxl6b0i.fsf@igel.home/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2024-12-09 10:00:25 -08:00
parent fac04efc5c
commit 32913f3482
1 changed files with 2 additions and 2 deletions
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4
kernel/futex/futex.h
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@ -265,11 +265,11 @@ static __always_inline int futex_read_inatomic(u32 *dest, u32 __user *from)
else if (!user_read_access_begin(from, sizeof(*from)))
return -EFAULT;
unsafe_get_user(val, from, Efault);
user_access_end();
user_read_access_end();
*dest = val;
return 0;
Efault:
user_access_end();
user_read_access_end();
return -EFAULT;
}