[PATCH 10/12] signal: Redefine signinfo so 64bit fields are possible

From: "Eric W. Beiderman" <ebiederm@xmission.com>
To: Marco Elver <elver@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Florian Weimer <fweimer@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Collingbourne <pcc@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	sparclinux <sparclinux@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: [PATCH 10/12] signal: Redefine signinfo so 64bit fields are possible
Date: Mon,  3 May 2021 15:38:12 -0500	[thread overview]
Message-ID: <20210503203814.25487-10-ebiederm@xmission.com> (raw)
In-Reply-To: <20210503203814.25487-1-ebiederm@xmission.com>

From: "Eric W. Biederman" <ebiederm@xmission.com>

The si_perf code really wants to add a u64 field.  This change enables
that by reorganizing the definition of siginfo_t, so that a 64bit
field can be added without increasing the alignment of other fields.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 arch/x86/kernel/signal_compat.c    |  9 +++----
 include/linux/compat.h             | 28 +++++++++++++-------
 include/uapi/asm-generic/siginfo.h | 42 ++++++++++++++++++++----------
 3 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index a9fcabd8a5e5..a5cd01c52dfb 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -17,8 +17,6 @@
  */
 static inline void signal_compat_build_tests(void)
 {
-	int _sifields_offset = offsetof(compat_siginfo_t, _sifields);
-
 	/*
 	 * If adding a new si_code, there is probably new data in
 	 * the siginfo.  Make sure folks bumping the si_code
@@ -40,8 +38,7 @@ static inline void signal_compat_build_tests(void)
 	 * in the ABI, of course.  Make sure none of them ever
 	 * move and are always at the beginning:
 	 */
-	BUILD_BUG_ON(offsetof(compat_siginfo_t, _sifields) != 3 * sizeof(int));
-#define CHECK_CSI_OFFSET(name)	  BUILD_BUG_ON(_sifields_offset != offsetof(compat_siginfo_t, _sifields.name))
+#define CHECK_CSI_OFFSET(name)	  BUILD_BUG_ON(0 != offsetof(compat_siginfo_t, _sifields.name))
 
 	BUILD_BUG_ON(offsetof(siginfo_t, si_signo) != 0);
 	BUILD_BUG_ON(offsetof(siginfo_t, si_errno) != 4);
@@ -63,8 +60,8 @@ static inline void signal_compat_build_tests(void)
 	 * structure stays within the padding size (checked
 	 * above).
 	 */
-#define CHECK_CSI_SIZE(name, size) BUILD_BUG_ON(size != sizeof(((compat_siginfo_t *)0)->_sifields.name))
-#define CHECK_SI_SIZE(name, size) BUILD_BUG_ON(size != sizeof(((siginfo_t *)0)->_sifields.name))
+#define CHECK_CSI_SIZE(name, size) BUILD_BUG_ON(((3*sizeof(int))+(size)) != sizeof(((compat_siginfo_t *)0)->_sifields.name))
+#define CHECK_SI_SIZE(name, size) BUILD_BUG_ON(((4*sizeof(int))+(size)) != sizeof(((siginfo_t *)0)->_sifields.name))
 
 	CHECK_CSI_OFFSET(_kill);
 	CHECK_CSI_SIZE  (_kill, 2*sizeof(int));
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 6af7bef15e94..d81493248bf3 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -158,27 +158,28 @@ typedef union compat_sigval {
 	compat_uptr_t	sival_ptr;
 } compat_sigval_t;
 
-typedef struct compat_siginfo {
-	int si_signo;
-#ifndef __ARCH_HAS_SWAPPED_SIGINFO
-	int si_errno;
-	int si_code;
-#else
-	int si_code;
-	int si_errno;
-#endif
+#define __COMPAT_SIGINFO_COMMON	\
+	___SIGINFO_COMMON;	\
+	int	_common_pad[__alignof__(compat_uptr_t) != __alignof__(int)]
 
+typedef struct compat_siginfo {
+	union {
+		struct {
+			__COMPAT_SIGINFO_COMMON;
+		};
 	union {
-		int _pad[128/sizeof(int) - 3];
+		int _pad[128/sizeof(int)];
 
 		/* kill() */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_pid_t _pid;	/* sender's pid */
 			__compat_uid32_t _uid;	/* sender's uid */
 		} _kill;
 
 		/* POSIX.1b timers */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_timer_t _tid;	/* timer id */
 			int _overrun;		/* overrun count */
 			compat_sigval_t _sigval;	/* same as below */
@@ -186,6 +187,7 @@ typedef struct compat_siginfo {
 
 		/* POSIX.1b signals */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_pid_t _pid;	/* sender's pid */
 			__compat_uid32_t _uid;	/* sender's uid */
 			compat_sigval_t _sigval;
@@ -193,6 +195,7 @@ typedef struct compat_siginfo {
 
 		/* SIGCHLD */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_pid_t _pid;	/* which child */
 			__compat_uid32_t _uid;	/* sender's uid */
 			int _status;		/* exit code */
@@ -203,6 +206,7 @@ typedef struct compat_siginfo {
 #ifdef CONFIG_X86_X32_ABI
 		/* SIGCHLD (x32 version) */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_pid_t _pid;	/* which child */
 			__compat_uid32_t _uid;	/* sender's uid */
 			int _status;		/* exit code */
@@ -213,6 +217,7 @@ typedef struct compat_siginfo {
 
 		/* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_uptr_t _addr;	/* faulting insn/memory ref. */
 #define __COMPAT_ADDR_BND_PKEY_PAD  (__alignof__(compat_uptr_t) < sizeof(short) ? \
 				     sizeof(short) : __alignof__(compat_uptr_t))
@@ -242,16 +247,19 @@ typedef struct compat_siginfo {
 
 		/* SIGPOLL */
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_long_t _band;	/* POLL_IN, POLL_OUT, POLL_MSG */
 			int _fd;
 		} _sigpoll;
 
 		struct {
+			__COMPAT_SIGINFO_COMMON;
 			compat_uptr_t _call_addr; /* calling user insn */
 			int _syscall;	/* triggering system call number */
 			unsigned int _arch;	/* AUDIT_ARCH_* of syscall */
 		} _sigsys;
 	} _sifields;
+	};
 } compat_siginfo_t;
 
 struct compat_rlimit {
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index e663bf117b46..1fcede623a73 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -29,15 +29,33 @@ typedef union sigval {
 #define __ARCH_SI_ATTRIBUTES
 #endif
 
+#ifndef __ARCH_HAS_SWAPPED_SIGINFO
+#define ___SIGINFO_COMMON	\
+	int	si_signo;	\
+	int	si_errno;	\
+	int	si_code
+#else
+#define ___SIGINFO_COMMON	\
+	int	si_signo;	\
+	int	si_code;	\
+	int	si_errno
+#endif /* __ARCH_HAS_SWAPPED_SIGINFO */
+
+#define __SIGINFO_COMMON	\
+	___SIGINFO_COMMON;	\
+	int	_common_pad[__alignof__(void *) != __alignof(int)]
+
 union __sifields {
 	/* kill() */
 	struct {
+		__SIGINFO_COMMON;
 		__kernel_pid_t _pid;	/* sender's pid */
 		__kernel_uid32_t _uid;	/* sender's uid */
 	} _kill;
 
 	/* POSIX.1b timers */
 	struct {
+		__SIGINFO_COMMON;
 		__kernel_timer_t _tid;	/* timer id */
 		int _overrun;		/* overrun count */
 		sigval_t _sigval;	/* same as below */
@@ -46,6 +64,7 @@ union __sifields {
 
 	/* POSIX.1b signals */
 	struct {
+		__SIGINFO_COMMON;
 		__kernel_pid_t _pid;	/* sender's pid */
 		__kernel_uid32_t _uid;	/* sender's uid */
 		sigval_t _sigval;
@@ -53,6 +72,7 @@ union __sifields {
 
 	/* SIGCHLD */
 	struct {
+		__SIGINFO_COMMON;
 		__kernel_pid_t _pid;	/* which child */
 		__kernel_uid32_t _uid;	/* sender's uid */
 		int _status;		/* exit code */
@@ -62,6 +82,7 @@ union __sifields {
 
 	/* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
 	struct {
+		__SIGINFO_COMMON;
 		void __user *_addr; /* faulting insn/memory ref. */
 #ifdef __ia64__
 		int _imm;		/* immediate value for "break" */
@@ -97,35 +118,28 @@ union __sifields {
 
 	/* SIGPOLL */
 	struct {
+		__SIGINFO_COMMON;
 		__ARCH_SI_BAND_T _band;	/* POLL_IN, POLL_OUT, POLL_MSG */
 		int _fd;
 	} _sigpoll;
 
 	/* SIGSYS */
 	struct {
+		__SIGINFO_COMMON;
 		void __user *_call_addr; /* calling user insn */
 		int _syscall;	/* triggering system call number */
 		unsigned int _arch;	/* AUDIT_ARCH_* of syscall */
 	} _sigsys;
 };
 
-#ifndef __ARCH_HAS_SWAPPED_SIGINFO
-#define __SIGINFO 			\
-struct {				\
-	int si_signo;			\
-	int si_errno;			\
-	int si_code;			\
-	union __sifields _sifields;	\
-}
-#else
+
 #define __SIGINFO 			\
-struct {				\
-	int si_signo;			\
-	int si_code;			\
-	int si_errno;			\
+union {					\
+	struct {			\
+		__SIGINFO_COMMON;	\
+	};				\
 	union __sifields _sifields;	\
 }
-#endif /* __ARCH_HAS_SWAPPED_SIGINFO */
 
 typedef struct siginfo {
 	union {
-- 
2.30.1

