Commit 4ce5f9c9 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

signal: Use a smaller struct siginfo in the kernel 



We reserve 128 bytes for struct siginfo but only use about 48 bytes on
64bit and 32 bytes on 32bit.  Someday we might use more but it is unlikely
to be anytime soon.

Userspace seems content with just enough bytes of siginfo to implement
sigqueue.  Or in the case of checkpoint/restart reinjecting signals
the kernel has sent.

Reducing the stack footprint and the work to copy siginfo around from
2 cachelines to 1 cachelines seems worth doing even if I don't have
benchmarks to show a performance difference.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent ae7795bc

include/linux/signal.h

+2 −0
Original line number Diff line number Diff line
@@ -22,6 +22,8 @@ static inline void clear_siginfo(kernel_siginfo_t *info) 
	memset(info, 0, sizeof(*info));

}



#define SI_EXPANSION_SIZE (sizeof(struct siginfo) - sizeof(struct kernel_siginfo))



int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);

int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);

include/linux/signal_types.h

+1 −4
Original line number Diff line number Diff line
@@ -10,10 +10,7 @@ 
#include <uapi/linux/signal.h>



typedef struct kernel_siginfo {

	union {

	__SIGINFO;

		int _si_pad[SI_MAX_SIZE/sizeof(int)];

	};

} kernel_siginfo_t;



/*

kernel/signal.c

+64 −18
Original line number Diff line number Diff line
@@ -2844,13 +2844,9 @@ COMPAT_SYSCALL_DEFINE2(rt_sigpending, compat_sigset_t __user *, uset, 
}

#endif



enum siginfo_layout siginfo_layout(int sig, int si_code)

{

	enum siginfo_layout layout = SIL_KILL;

	if ((si_code > SI_USER) && (si_code < SI_KERNEL)) {

static const struct {

	unsigned char limit, layout;

		} filter[] = {

} sig_sicodes[] = {

	[SIGILL]  = { NSIGILL,  SIL_FAULT },

	[SIGFPE]  = { NSIGFPE,  SIL_FAULT },

	[SIGSEGV] = { NSIGSEGV, SIL_FAULT },
@@ -2863,8 +2859,33 @@ enum siginfo_layout siginfo_layout(int sig, int si_code) 
	[SIGPOLL] = { NSIGPOLL, SIL_POLL },

	[SIGSYS]  = { NSIGSYS,  SIL_SYS },

};

		if ((sig < ARRAY_SIZE(filter)) && (si_code <= filter[sig].limit)) {

			layout = filter[sig].layout;



static bool known_siginfo_layout(int sig, int si_code)

{

	if (si_code == SI_KERNEL)

		return true;

	else if ((si_code > SI_USER)) {

		if (sig_specific_sicodes(sig)) {

			if (si_code <= sig_sicodes[sig].limit)

				return true;

		}

		else if (si_code <= NSIGPOLL)

			return true;

	}

	else if (si_code >= SI_DETHREAD)

		return true;

	else if (si_code == SI_ASYNCNL)

		return true;

	return false;

}



enum siginfo_layout siginfo_layout(int sig, int si_code)

{

	enum siginfo_layout layout = SIL_KILL;

	if ((si_code > SI_USER) && (si_code < SI_KERNEL)) {

		if ((sig < ARRAY_SIZE(sig_sicodes)) &&

		    (si_code <= sig_sicodes[sig].limit)) {

			layout = sig_sicodes[sig].layout;

			/* Handle the exceptions */

			if ((sig == SIGBUS) &&

			    (si_code >= BUS_MCEERR_AR) && (si_code <= BUS_MCEERR_AO))
@@ -2889,17 +2910,42 @@ enum siginfo_layout siginfo_layout(int sig, int si_code) 
	return layout;

}



static inline char __user *si_expansion(const siginfo_t __user *info)

{

	return ((char __user *)info) + sizeof(struct kernel_siginfo);

}



int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from)

{

	char __user *expansion = si_expansion(to);

	if (copy_to_user(to, from , sizeof(struct kernel_siginfo)))

		return -EFAULT;

	if (clear_user(expansion, SI_EXPANSION_SIZE))

		return -EFAULT;

	return 0;

}



int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from)

{

	if (copy_from_user(to, from, sizeof(struct siginfo)))

	if (copy_from_user(to, from, sizeof(struct kernel_siginfo)))

		return -EFAULT;

	if (unlikely(!known_siginfo_layout(to->si_signo, to->si_code))) {

		char __user *expansion = si_expansion(from);

		char buf[SI_EXPANSION_SIZE];

		int i;

		/*

		 * An unknown si_code might need more than

		 * sizeof(struct kernel_siginfo) bytes.  Verify all of the

		 * extra bytes are 0.  This guarantees copy_siginfo_to_user

		 * will return this data to userspace exactly.

		 */

		if (copy_from_user(&buf, expansion, SI_EXPANSION_SIZE))

			return -EFAULT;

		for (i = 0; i < SI_EXPANSION_SIZE; i++) {

			if (buf[i] != 0)

				return -E2BIG;

		}

	}

	return 0;

}

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