[PATCH v1 0/5] Reenable might_sleep() checks for might_fault()

David Hildenbrand
2014-12-05T11:18:20Z

I recently discovered that might_fault() doesn't call might_sleep() anymore.
Therefore bugs like:
spin_lock(&lock);
rc = copy_to_user(...);
spin_unlock(&lock);
would not be detected with CONFIG_DEBUG_ATOMIC_SLEEP. The code was changed to
disable false positives for code like:
pagefault_disable();
rc = copy_to_user(...);
pagefault_enable();

Until now, pagefault_disable() and pagefault_enable() simply modified the
preempt count, therefore telling the pagefault handler that the context is
atomic and sleeping is disallowed.

In order to reenable might_sleep() checks for the correct path, we need a way to
detect whether we run in a pagefault_disable() context.

This series therefore introduces a separate pagefault_count and uses it to count
the levels of pagefault_disable() per thread. might_sleep() checks are
reactivated for the !pagefault_disable() path.

So this should now work:
spin_lock(&lock); /* also if left away */
pagefault_disable()
rc = copy_to_user(...);
pagefault_enable();
spin_unlock(&lock);
And this should report a warning again:
spin_lock(&lock);
rc = copy_to_user(...);
spin_unlock(&lock);

Please note that this series will not completely split the handling of
pagefault_disable() and the preempt count. This will be done in another series.
Purpose of this series is to reenable might_sleep() checks for might_fault(),
avoiding to produce false positives.

Cross compiled on powerpc, arm, sparc, sparc64, arm64, x86_64, i386, mips,
alpha, ia64, xtensa, m68k, microblaze.

Tested on s390. Would be good to get some feedback on the ASM offsets for m32r,
sparc and xtensa (or if I should simply move the count to the end of the struct
for these archs ...).

Thanks!

David

David Hildenbrand (5):
uaccess: add pagefault_count to thread_info
uaccess: count pagefault_disable() levels in pagefault_count
mm, uaccess: trigger might_sleep() in might_fault() when pagefaults
are disabled
uaccess: clearify that uaccess may only sleep if pagefaults are not
disabled
uaccess: CONFIG_DEBUG_PAGEFAULT_COUNT to debug pagefault_count

arch/alpha/include/asm/thread_info.h | 1 +
arch/arc/include/asm/thread_info.h | 1 +
arch/arm/include/asm/thread_info.h | 1 +
arch/arm64/include/asm/thread_info.h | 1 +
arch/avr32/include/asm/thread_info.h | 1 +
arch/avr32/include/asm/uaccess.h | 12 +++++---
arch/blackfin/include/asm/thread_info.h | 1 +
arch/c6x/include/asm/thread_info.h | 1 +
arch/cris/include/asm/thread_info.h | 1 +
arch/frv/include/asm/thread_info.h | 1 +
arch/hexagon/include/asm/thread_info.h | 1 +
arch/hexagon/include/asm/uaccess.h | 3 +-
arch/ia64/include/asm/thread_info.h | 1 +
arch/m32r/include/asm/thread_info.h | 5 +--
arch/m32r/include/asm/uaccess.h | 30 ++++++++++++------
arch/m68k/include/asm/thread_info.h | 1 +
arch/metag/include/asm/thread_info.h | 1 +
arch/microblaze/include/asm/thread_info.h | 1 +
arch/microblaze/include/asm/uaccess.h | 6 ++--
arch/mips/include/asm/thread_info.h | 1 +
arch/mips/include/asm/uaccess.h | 45 ++++++++++++++++++---------
arch/mn10300/include/asm/thread_info.h | 1 +
arch/openrisc/include/asm/thread_info.h | 1 +
arch/parisc/include/asm/thread_info.h | 1 +
arch/powerpc/include/asm/thread_info.h | 1 +
arch/s390/include/asm/thread_info.h | 1 +
arch/s390/include/asm/uaccess.h | 15 ++++++---
arch/score/include/asm/thread_info.h | 1 +
arch/score/include/asm/uaccess.h | 15 ++++++---
arch/sh/include/asm/thread_info.h | 1 +
arch/sparc/include/asm/thread_info_32.h | 20 ++++++------
arch/sparc/include/asm/thread_info_64.h | 17 ++++++-----
arch/tile/include/asm/thread_info.h | 1 +
arch/tile/include/asm/uaccess.h | 21 ++++++++-----
arch/um/include/asm/thread_info.h | 1 +
arch/unicore32/include/asm/thread_info.h | 1 +
arch/x86/include/asm/thread_info.h | 1 +
arch/x86/include/asm/uaccess.h | 15 ++++++---
arch/x86/include/asm/uaccess_32.h | 6 ++--
arch/x86/lib/usercopy_32.c | 6 ++--
arch/xtensa/include/asm/thread_info.h | 5 +--
include/linux/kernel.h | 3 +-
include/linux/uaccess.h | 51 ++++++++++++++++++++++++++-----
lib/Kconfig.debug | 9 ++++++
lib/strnlen_user.c | 6 ++--
mm/maccess.c | 11 +++++++
mm/memory.c | 19 +++++-------
47 files changed, 245 insertions(+), 101 deletions(-)

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1.8.5.5