The following commit has been merged into the perf/core branch of tip: Commit-ID: 3ddb3fd8cdb0a6c11b7c8d91ba42d84c4ea3cc43 Gitweb: https://git.kernel.org/tip/3ddb3fd8cdb0a6c11b7c8d91ba42d84c4ea3cc43 Author: Marco Elver <elver@xxxxxxxxxx> AuthorDate: Thu, 22 Apr 2021 21:18:22 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Fri, 23 Apr 2021 09:03:16 +02:00 signal, perf: Fix siginfo_t by avoiding u64 on 32-bit architectures The alignment of a structure is that of its largest member. On architectures like 32-bit Arm (but not e.g. 32-bit x86) 64-bit integers will require 64-bit alignment and not its natural word size. This means that there is no portable way to add 64-bit integers to siginfo_t on 32-bit architectures without breaking the ABI, because siginfo_t does not yet (and therefore likely never will) contain 64-bit fields on 32-bit architectures. Adding a 64-bit integer could change the alignment of the union after the 3 initial int si_signo, si_errno, si_code, thus introducing 4 bytes of padding shifting the entire union, which would break the ABI. One alternative would be to use the __packed attribute, however, it is non-standard C. Given siginfo_t has definitions outside the Linux kernel in various standard libraries that can be compiled with any number of different compilers (not just those we rely on), using non-standard attributes on siginfo_t should be avoided to ensure portability. In the case of the si_perf field, word size is sufficient since there is no exact requirement on size, given the data it contains is user-defined via perf_event_attr::sig_data. On 32-bit architectures, any excess bits of perf_event_attr::sig_data will therefore be truncated when copying into si_perf. Since si_perf is intended to disambiguate events (e.g. encoding relevant information if there are more events of the same type), 32 bits should provide enough entropy to do so on 32-bit architectures. For 64-bit architectures, no change is intended. Fixes: fb6cc127e0b6 ("signal: Introduce TRAP_PERF si_code and si_perf to siginfo") Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Reported-by: Jon Hunter <jonathanh@xxxxxxxxxx> Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20210422191823.79012-1-elver@xxxxxxxxxx --- include/linux/compat.h | 2 +- include/uapi/asm-generic/siginfo.h | 2 +- tools/testing/selftests/perf_events/sigtrap_threads.c | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/compat.h b/include/linux/compat.h index c8821d9..f0d2dd3 100644 --- a/include/linux/compat.h +++ b/include/linux/compat.h @@ -237,7 +237,7 @@ typedef struct compat_siginfo { u32 _pkey; } _addr_pkey; /* used when si_code=TRAP_PERF */ - compat_u64 _perf; + compat_ulong_t _perf; }; } _sigfault; diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index d0bb912..03d6f6d 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -92,7 +92,7 @@ union __sifields { __u32 _pkey; } _addr_pkey; /* used when si_code=TRAP_PERF */ - __u64 _perf; + unsigned long _perf; }; } _sigfault; diff --git a/tools/testing/selftests/perf_events/sigtrap_threads.c b/tools/testing/selftests/perf_events/sigtrap_threads.c index 9c0fd44..78ddf5e 100644 --- a/tools/testing/selftests/perf_events/sigtrap_threads.c +++ b/tools/testing/selftests/perf_events/sigtrap_threads.c @@ -44,7 +44,7 @@ static struct { } ctx; /* Unique value to check si_perf is correctly set from perf_event_attr::sig_data. */ -#define TEST_SIG_DATA(addr) (~(uint64_t)(addr)) +#define TEST_SIG_DATA(addr) (~(unsigned long)(addr)) static struct perf_event_attr make_event_attr(bool enabled, volatile void *addr) {
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