signal: Introduce TRAP_PERF si_code and si_perf to siginfo

Introduces the TRAP_PERF si_code, and associated siginfo_t field
si_perf. These will be used by the perf event subsystem to send signals
(if requested) to the task where an event occurred.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k
Acked-by: Arnd Bergmann <arnd@arndb.de> # asm-generic
Link: https://lkml.kernel.org/r/20210408103605.1676875-6-elver@google.com

arch/m68k/kernel/signal.c

@@ -622,6 +622,9 @@ static inline void siginfo_build_tests(void)
 	/* _sigfault._addr_pkey */
 	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x12);
 
+	/* _sigfault._perf */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_perf) != 0x10);
+
 	/* _sigpoll */
 	BUILD_BUG_ON(offsetof(siginfo_t, si_band)   != 0x0c);
 	BUILD_BUG_ON(offsetof(siginfo_t, si_fd)     != 0x10);

arch/x86/kernel/signal_compat.c

@@ -29,7 +29,7 @@ static inline void signal_compat_build_tests(void)
 	BUILD_BUG_ON(NSIGFPE  != 15);
 	BUILD_BUG_ON(NSIGSEGV != 9);
 	BUILD_BUG_ON(NSIGBUS  != 5);
-	BUILD_BUG_ON(NSIGTRAP != 5);
+	BUILD_BUG_ON(NSIGTRAP != 6);
 	BUILD_BUG_ON(NSIGCHLD != 6);
 	BUILD_BUG_ON(NSIGSYS  != 2);
 
@@ -138,6 +138,9 @@ static inline void signal_compat_build_tests(void)
 	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x20);
 	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pkey) != 0x14);
 
+	BUILD_BUG_ON(offsetof(siginfo_t, si_perf) != 0x18);
+	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_perf) != 0x10);
+
 	CHECK_CSI_OFFSET(_sigpoll);
 	CHECK_CSI_SIZE  (_sigpoll, 2*sizeof(int));
 	CHECK_SI_SIZE   (_sigpoll, 4*sizeof(int));

fs/signalfd.c

@@ -134,6 +134,10 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 #endif
 		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
 		break;
+	case SIL_PERF_EVENT:
+		new.ssi_addr = (long) kinfo->si_addr;
+		new.ssi_perf = kinfo->si_perf;
+		break;
 	case SIL_CHLD:
 		new.ssi_pid    = kinfo->si_pid;
 		new.ssi_uid    = kinfo->si_uid;

include/linux/compat.h

@@ -236,6 +236,8 @@ typedef struct compat_siginfo {
 					char _dummy_pkey[__COMPAT_ADDR_BND_PKEY_PAD];
 					u32 _pkey;
 				} _addr_pkey;
+				/* used when si_code=TRAP_PERF */
+				compat_u64 _perf;
 			};
 		} _sigfault;
 

include/linux/signal.h

@@ -43,6 +43,7 @@ enum siginfo_layout {
 	SIL_FAULT_MCEERR,
 	SIL_FAULT_BNDERR,
 	SIL_FAULT_PKUERR,
+	SIL_PERF_EVENT,
 	SIL_CHLD,
 	SIL_RT,
 	SIL_SYS,

include/uapi/asm-generic/siginfo.h

@@ -91,6 +91,8 @@ union __sifields {
 				char _dummy_pkey[__ADDR_BND_PKEY_PAD];
 				__u32 _pkey;
 			} _addr_pkey;
+			/* used when si_code=TRAP_PERF */
+			__u64 _perf;
 		};
 	} _sigfault;
 
@@ -155,6 +157,7 @@ typedef struct siginfo {
 #define si_lower	_sifields._sigfault._addr_bnd._lower
 #define si_upper	_sifields._sigfault._addr_bnd._upper
 #define si_pkey		_sifields._sigfault._addr_pkey._pkey
+#define si_perf		_sifields._sigfault._perf
 #define si_band		_sifields._sigpoll._band
 #define si_fd		_sifields._sigpoll._fd
 #define si_call_addr	_sifields._sigsys._call_addr
@@ -253,7 +256,8 @@ typedef struct siginfo {
 #define TRAP_BRANCH     3	/* process taken branch trap */
 #define TRAP_HWBKPT     4	/* hardware breakpoint/watchpoint */
 #define TRAP_UNK	5	/* undiagnosed trap */
-#define NSIGTRAP	5
+#define TRAP_PERF	6	/* perf event with sigtrap=1 */
+#define NSIGTRAP	6
 
 /*
  * There is an additional set of SIGTRAP si_codes used by ptrace

include/uapi/linux/signalfd.h

@@ -39,6 +39,8 @@ struct signalfd_siginfo {
 	__s32 ssi_syscall;
 	__u64 ssi_call_addr;
 	__u32 ssi_arch;
+	__u32 __pad3;
+	__u64 ssi_perf;
 
 	/*
 	 * Pad strcture to 128 bytes. Remember to update the
@@ -49,7 +51,7 @@ struct signalfd_siginfo {
 	 * comes out of a read(2) and we really don't want to have
 	 * a compat on read(2).
 	 */
-	__u8 __pad[28];
+	__u8 __pad[16];
 };
 
 

kernel/signal.c

@@ -1199,6 +1199,7 @@ static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)
 	case SIL_FAULT_MCEERR:
 	case SIL_FAULT_BNDERR:
 	case SIL_FAULT_PKUERR:
+	case SIL_PERF_EVENT:
 	case SIL_SYS:
 		ret = false;
 		break;
@@ -2531,6 +2532,7 @@ static void hide_si_addr_tag_bits(struct ksignal *ksig)
 	case SIL_FAULT_MCEERR:
 	case SIL_FAULT_BNDERR:
 	case SIL_FAULT_PKUERR:
+	case SIL_PERF_EVENT:
 		ksig->info.si_addr = arch_untagged_si_addr(
 			ksig->info.si_addr, ksig->sig, ksig->info.si_code);
 		break;
@@ -3333,6 +3335,10 @@ void copy_siginfo_to_external32(struct compat_siginfo *to,
 #endif
 		to->si_pkey = from->si_pkey;
 		break;
+	case SIL_PERF_EVENT:
+		to->si_addr = ptr_to_compat(from->si_addr);
+		to->si_perf = from->si_perf;
+		break;
 	case SIL_CHLD:
 		to->si_pid = from->si_pid;
 		to->si_uid = from->si_uid;
@@ -3413,6 +3419,10 @@ static int post_copy_siginfo_from_user32(kernel_siginfo_t *to,
 #endif
 		to->si_pkey = from->si_pkey;
 		break;
+	case SIL_PERF_EVENT:
+		to->si_addr = compat_ptr(from->si_addr);
+		to->si_perf = from->si_perf;
+		break;
 	case SIL_CHLD:
 		to->si_pid    = from->si_pid;
 		to->si_uid    = from->si_uid;
@@ -4593,6 +4603,7 @@ static inline void siginfo_buildtime_checks(void)
 	CHECK_OFFSET(si_lower);
 	CHECK_OFFSET(si_upper);
 	CHECK_OFFSET(si_pkey);
+	CHECK_OFFSET(si_perf);
 
 	/* sigpoll */
 	CHECK_OFFSET(si_band);