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authorDave Hansen <dave.hansen@linux.intel.com>2016-03-01 04:54:51 -0800
committerIngo Molnar <mingo@kernel.org>2016-03-05 15:00:06 +0100
commit49cd53bf14aeb471c4a2682300dfc05ef2fd09f2 (patch)
tree5b1dfde4216c825a2fe104ada4c6fddd17f93915 /include/uapi/asm-generic/siginfo.h
parente21555436f196c241503c7c6240272e57783235c (diff)
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/asm-generic/siginfo.h')
-rw-r--r--include/uapi/asm-generic/siginfo.h2
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;

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