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From:   ebiederm@xmission.com (Eric W. Biederman)
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>
References: <m14kfjh8et.fsf_-_@fess.ebiederm.org>
        <20210503203814.25487-1-ebiederm@xmission.com>
        <20210503203814.25487-10-ebiederm@xmission.com>
Date:   Mon, 03 May 2021 16:04:05 -0500
In-Reply-To: <20210503203814.25487-10-ebiederm@xmission.com> (Eric
        W. Beiderman's message of "Mon, 3 May 2021 15:38:12 -0500")
Message-ID: <m1o8drfs1m.fsf@fess.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
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Subject: Re: [PATCH 10/12] signal: Redefine signinfo so 64bit fields are possible
Precedence: bulk

"Eric W. Beiderman" <ebiederm@xmission.com> writes:

> 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.

I decided to include this change because it is not that complicated,
and it allows si_perf_data to have the definition that was originally
desired.

If this looks difficult to make in the userspace definitions,
or is otherwise a problem I don't mind dropping this change.  I just
figured since it was not too difficult and we are changing things
anyway I should try for everything.

Eric


> 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 {