siginfo: Move si_trapno inside the union inside _si_fault

It turns out that linux uses si_trapno very sparingly, and as such it
can be considered extra information for a very narrow selection of
signals, rather than information that is present with every fault
reported in siginfo.

As such move si_trapno inside the union inside of _si_fault.  This
results in no change in placement, and makes it eaiser
to extend _si_fault in the future as this reduces the number of
special cases.  In particular with si_trapno included in the union it
is no longer a concern that the union must be pointer aligned on most
architectures because the union follows immediately after si_addr
which is a pointer.

This change results in a difference in siginfo field placement on
sparc and alpha for the fields si_addr_lsb, si_lower, si_upper,
si_pkey, and si_perf.  These architectures do not implement the
signals that would use si_addr_lsb, si_lower, si_upper, si_pkey, and
si_perf.  Further these architecture have not yet implemented the
userspace that would use si_perf.

The point of this change is in fact to correct these placement issues
before sparc or alpha grow userspace that cares.  This change was
discussed[1] and the agreement is that this change is currently safe.

[1]: https://lkml.kernel.org/r/CAK8P3a0+uKYwL1NhY6Hvtieghba2hKYGD6hcKx5n8=4Gtt+pHA@mail.gmail.com
Acked-by: Marco Elver <elver@google.com>
v1: https://lkml.kernel.org/r/m1tunns7yf.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/20210505141101.11519-5-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20210517195748.8880-1-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 0e5d0a7..a9fcabd 100644 (file)
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -127,6 +127,9 @@ static inline void signal_compat_build_tests(void)
        BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x10);
        BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr) != 0x0C);
 
+       BUILD_BUG_ON(offsetof(siginfo_t, si_trapno) != 0x18);
+       BUILD_BUG_ON(offsetof(compat_siginfo_t, si_trapno) != 0x10);
+
        BUILD_BUG_ON(offsetof(siginfo_t, si_addr_lsb) != 0x18);
        BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr_lsb) != 0x10);
 

diff --git a/include/linux/compat.h b/include/linux/compat.h
index f0d2dd3..6af7bef 100644 (file)
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -214,12 +214,11 @@ typedef struct compat_siginfo {
                /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
                struct {
                        compat_uptr_t _addr;    /* faulting insn/memory ref. */
-#ifdef __ARCH_SI_TRAPNO
-                       int _trapno;    /* TRAP # which caused the signal */
-#endif
 #define __COMPAT_ADDR_BND_PKEY_PAD  (__alignof__(compat_uptr_t) < sizeof(short) ? \
                                     sizeof(short) : __alignof__(compat_uptr_t))
                        union {
+                               /* used on alpha and sparc */
+                               int _trapno;    /* TRAP # which caused the signal */
                                /*
                                 * used when si_code=BUS_MCEERR_AR or
                                 * used when si_code=BUS_MCEERR_AO

diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 03d6f6d..e663bf1 100644 (file)
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -63,9 +63,6 @@ union __sifields {
        /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
        struct {
                void __user *_addr; /* faulting insn/memory ref. */
-#ifdef __ARCH_SI_TRAPNO
-               int _trapno;    /* TRAP # which caused the signal */
-#endif
 #ifdef __ia64__
                int _imm;               /* immediate value for "break" */
                unsigned int _flags;    /* see ia64 si_flags */
@@ -75,6 +72,8 @@ union __sifields {
 #define __ADDR_BND_PKEY_PAD  (__alignof__(void *) < sizeof(short) ? \
                              sizeof(short) : __alignof__(void *))
                union {
+                       /* used on alpha and sparc */
+                       int _trapno;    /* TRAP # which caused the signal */
                        /*
                         * used when si_code=BUS_MCEERR_AR or
                         * used when si_code=BUS_MCEERR_AO
@@ -150,9 +149,7 @@ typedef struct siginfo {
 #define si_int         _sifields._rt._sigval.sival_int
 #define si_ptr         _sifields._rt._sigval.sival_ptr
 #define si_addr                _sifields._sigfault._addr
-#ifdef __ARCH_SI_TRAPNO
 #define si_trapno      _sifields._sigfault._trapno
-#endif
 #define si_addr_lsb    _sifields._sigfault._addr_lsb
 #define si_lower       _sifields._sigfault._addr_bnd._lower
 #define si_upper       _sifields._sigfault._addr_bnd._upper

diff --git a/kernel/signal.c b/kernel/signal.c
index c3017aa..65888ae 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4607,6 +4607,7 @@ static inline void siginfo_buildtime_checks(void)
 
        /* sigfault */
        CHECK_OFFSET(si_addr);
+       CHECK_OFFSET(si_trapno);
        CHECK_OFFSET(si_addr_lsb);
        CHECK_OFFSET(si_lower);
        CHECK_OFFSET(si_upper);