Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 3 Mar 2016 08:53:08 -0800 | From | tip-bot for Dave Hansen <> | Subject | [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field |
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Commit-ID: 16bc7477807393efb5b81f875888ee9221ead3a1 Gitweb: http://git.kernel.org/tip/16bc7477807393efb5b81f875888ee9221ead3a1 Author: Dave Hansen <dave.hansen@linux.intel.com> AuthorDate: Tue, 1 Mar 2016 04:54:51 -0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 3 Mar 2016 16:44:21 +0100
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 (this is rare, most 32-bit platforms align it to 4 bytes), 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> --- arch/ia64/include/uapi/asm/siginfo.h | 2 +- arch/mips/include/uapi/asm/siginfo.h | 2 +- include/uapi/asm-generic/siginfo.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/ia64/include/uapi/asm/siginfo.h b/arch/ia64/include/uapi/asm/siginfo.h index 0151cfa..f72bf01 100644 --- a/arch/ia64/include/uapi/asm/siginfo.h +++ b/arch/ia64/include/uapi/asm/siginfo.h @@ -70,7 +70,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; diff --git a/arch/mips/include/uapi/asm/siginfo.h b/arch/mips/include/uapi/asm/siginfo.h index 6f4edf0..cc49dc2 100644 --- a/arch/mips/include/uapi/asm/siginfo.h +++ b/arch/mips/include/uapi/asm/siginfo.h @@ -93,7 +93,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 90384d5..1abaf62 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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