Update changelog with better description of the issue from Ingo. -- From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Stephen Rothwell reported: http://lkml.kernel.org/r/20160226164406.065a1ffc@xxxxxxxxxxxxxxxx that the Memory Protection Keys patches from the tip tree broke a build-time check on an ARM build because they changed the ABI of siginfo. 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 is guaranteed to union well with the pointers from _addr_bnd. It is also plenty large enough to store the 16-bit pkey we have today on x86. I also shouldn't have been using a u64 in a userspace API to begin with. Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults") Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Acked-by: Stehen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: linux-next@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: Helge Deller <deller@xxxxxx> --- b/arch/ia64/include/uapi/asm/siginfo.h | 2 +- b/arch/mips/include/uapi/asm/siginfo.h | 2 +- b/include/uapi/asm-generic/siginfo.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff -puN include/uapi/asm-generic/siginfo.h~pkeys-101-fix-siginfo include/uapi/asm-generic/siginfo.h --- a/include/uapi/asm-generic/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.327228965 -0800 +++ b/include/uapi/asm-generic/siginfo.h 2016-02-29 09:22:45.333229241 -0800 @@ -98,7 +98,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; diff -puN arch/mips/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo arch/mips/include/uapi/asm/siginfo.h --- a/arch/mips/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.330229103 -0800 +++ b/arch/mips/include/uapi/asm/siginfo.h 2016-02-29 09:22:45.333229241 -0800 @@ -93,7 +93,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; diff -puN arch/ia64/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo arch/ia64/include/uapi/asm/siginfo.h --- a/arch/ia64/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.331229149 -0800 +++ b/arch/ia64/include/uapi/asm/siginfo.h 2016-02-29 09:22:45.333229241 -0800 @@ -70,7 +70,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; _ -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
