summaryrefslogtreecommitdiff
path: root/include/linux/compat.h
diff options
context:
space:
mode:
authorMarco Elver <elver@google.com>2021-04-22 21:18:22 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-04-23 09:03:16 +0200
commit3ddb3fd8cdb0a6c11b7c8d91ba42d84c4ea3cc43 (patch)
tree458583355f514c9ce5e4d9bba961ce02c0e71583 /include/linux/compat.h
parent32d35c4a96ec79446f0d7be308a6eb248b507a0b (diff)
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@samsung.com> Reported-by: Jon Hunter <jonathanh@nvidia.com> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> Tested-by: Jon Hunter <jonathanh@nvidia.com> Link: https://lkml.kernel.org/r/20210422191823.79012-1-elver@google.com
Diffstat (limited to 'include/linux/compat.h')
-rw-r--r--include/linux/compat.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/compat.h b/include/linux/compat.h
index c8821d966812..f0d2dd35d408 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;