linux/include
Will Deacon ec6931b281 word-at-a-time: avoid undefined behaviour in zero_bytemask macro
The asm-generic, big-endian version of zero_bytemask creates a mask of
bytes preceding the first zero-byte by left shifting ~0ul based on the
position of the first zero byte.

Unfortunately, if the first (top) byte is zero, the output of
prep_zero_mask has only the top bit set, resulting in undefined C
behaviour as we shift left by an amount equal to the width of the type.
As it happens, GCC doesn't manage to spot this through the call to fls(),
but the issue remains if architectures choose to implement their shift
instructions differently.

An example would be arch/arm/ (AArch32), where LSL Rd, Rn, #32 results
in Rd == 0x0, whilst on arch/arm64 (AArch64) LSL Xd, Xn, #64 results in
Xd == Xn.

Rather than check explicitly for the problematic shift, this patch adds
an extra shift by 1, replacing fls with __fls. Since zero_bytemask is
never called with a zero argument (has_zero() is used to check the data
first), we don't need to worry about calling __fls(0), which is
undefined.

Cc: <stable@vger.kernel.org>
Cc: Victor Kamensky <victor.kamensky@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-04-27 15:20:05 -07:00
..
acpi IOMMU Upates for Linux v3.15 2014-04-05 18:46:26 -07:00
asm-generic word-at-a-time: avoid undefined behaviour in zero_bytemask macro 2014-04-27 15:20:05 -07:00
clocksource
crypto
drm Merge branch 'drm-next-3.15-wip' of git://people.freedesktop.org/~deathsimple/linux into drm-next 2014-04-19 11:16:02 +10:00
dt-bindings dt: tegra: remove non-existent clock IDs 2014-04-24 15:37:08 +02:00
keys
kvm
linux Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-04-27 11:21:03 -07:00
math-emu
media [media] rc-core: remove generic scancode filter 2014-04-06 11:30:29 -03:00
memory
misc
net net: sctp: cache auth_enable per endpoint 2014-04-18 18:32:00 -04:00
pcmcia
ras
rdma Merge branches 'core', 'cxgb4', 'ip-roce', 'iser', 'misc', 'mlx4', 'nes', 'ocrdma', 'qib', 'sgwrapper', 'srp' and 'usnic' into for-next 2014-04-03 08:30:17 -07:00
rxrpc
scsi scsi: Make sure cmd_flags are 64-bit 2014-04-09 20:26:20 -06:00
sound ALSA: cs8427: separate HW initialization 2014-04-03 14:59:48 +02:00
target target/sbc: Add sbc_dif_read_strip software emulation 2014-04-07 01:48:57 -07:00
trace These are regression and bug fixes for ext4. 2014-04-20 20:43:47 -07:00
uapi File locking related bugfixes for v3.15 (pile #2) 2014-04-25 12:40:32 -07:00
video fbdev changes for 3.15 (OMAP) 2014-04-07 10:47:51 -07:00
xen
Kbuild