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author | Dave Hansen <dave.hansen@linux.intel.com> | 2016-03-01 04:54:51 -0800 |
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committer | Ingo Molnar <mingo@kernel.org> | 2016-03-05 15:00:06 +0100 |
commit | 49cd53bf14aeb471c4a2682300dfc05ef2fd09f2 (patch) | |
tree | 5b1dfde4216c825a2fe104ada4c6fddd17f93915 /include/uapi | |
parent | e21555436f196c241503c7c6240272e57783235c (diff) | |
download | linux-49cd53bf14aeb471c4a2682300dfc05ef2fd09f2.tar.gz linux-49cd53bf14aeb471c4a2682300dfc05ef2fd09f2.tar.bz2 linux-49cd53bf14aeb471c4a2682300dfc05ef2fd09f2.zip |
mm/pkeys: Fix siginfo ABI breakage caused by new u64 field
Stephen Rothwell reported this linux-next build failure:
http://lkml.kernel.org/r/20160226164406.065a1ffc@canb.auug.org.au
... caused by the Memory Protection Keys patches from the tip tree triggering
a newly introduced build-time sanity check on an ARM build, because they changed
the ABI of siginfo in an unexpected way.
If u64 has a natural alignment of 8 bytes (which is the case on most mainstream
platforms, with the notable exception of x86-32), then the leadup to the
_sifields union matters:
typedef struct siginfo {
int si_signo;
int si_errno;
int si_code;
union {
...
} _sifields;
} __ARCH_SI_ATTRIBUTES siginfo_t;
Note how the first 3 fields give us 12 bytes, so _sifields is not 8
naturally bytes aligned.
Before the _pkey field addition the largest element of _sifields (on
32-bit platforms) was 32 bits. With the u64 added, the minimum alignment
requirement increased to 8 bytes on those (rare) 32-bit platforms. Thus
GCC padded the space after si_code with 4 extra bytes, and shifted all
_sifields offsets by 4 bytes - breaking the ABI of all of those
remaining fields.
On 64-bit platforms this problem was hidden due to _sifields already
having numerous fields with natural 8 bytes alignment (pointers).
To fix this, we replace the u64 with an '__u32'. The __u32 does not
increase the minimum alignment requirement of the union, and it is
also large enough to store the 16-bit pkey we have today on x86.
Reported-by: Stehen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Stehen Rothwell <sfr@canb.auug.org.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: Helge Deller <deller@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-next@vger.kernel.org
Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults")
Link: http://lkml.kernel.org/r/20160301125451.02C7426D@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/uapi')
-rw-r--r-- | include/uapi/asm-generic/siginfo.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 90384d55225b..1abaf62c86fc 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -98,7 +98,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; |