Commit 6ac05e83 authored by Peter Collingbourne's avatar Peter Collingbourne Committed by Eric W. Biederman
Browse files

signal: define the SA_EXPOSE_TAGBITS bit in sa_flags 



Architectures that support address tagging, such as arm64, may want to
expose fault address tag bits to the signal handler to help diagnose
memory errors. However, these bits have not been previously set,
and their presence may confuse unaware user applications. Therefore,
introduce a SA_EXPOSE_TAGBITS flag bit in sa_flags that a signal
handler may use to explicitly request that the bits are set.

The generic signal handler APIs expect to receive tagged addresses.
Architectures may specify how to untag addresses in the case where
SA_EXPOSE_TAGBITS is clear by defining the arch_untagged_si_addr
function.

Signed-off-by: default avatarPeter Collingbourne <pcc@google.com>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Link: https://linux-review.googlesource.com/id/I16dd0ed2081f091fce97be0190cb8caa874c26cb
Link: https://lkml.kernel.org/r/13cf24d00ebdd8e1f55caf1821c7c29d54100191.1605904350.git.pcc@google.com


Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent a54f0dfd

include/linux/signal.h

+14 −0
Original line number Diff line number Diff line
@@ -469,4 +469,18 @@ struct seq_file; 
extern void render_sigset_t(struct seq_file *, const char *, sigset_t *);

#endif



#ifndef arch_untagged_si_addr

/*

 * Given a fault address and a signal and si_code which correspond to the

 * _sigfault union member, returns the address that must appear in si_addr if

 * the signal handler does not have SA_EXPOSE_TAGBITS enabled in sa_flags.

 */

static inline void __user *arch_untagged_si_addr(void __user *addr,

						 unsigned long sig,

						 unsigned long si_code)

{

	return addr;

}

#endif



#endif /* _LINUX_SIGNAL_H */

include/linux/signal_types.h

+1 −1
Original line number Diff line number Diff line
@@ -78,6 +78,6 @@ struct ksignal { 


#define UAPI_SA_FLAGS                                                          \

	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \

	 SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS)

	 SA_NODEFER | SA_RESETHAND | SA_EXPOSE_TAGBITS | __ARCH_UAPI_SA_FLAGS)



#endif /* _LINUX_SIGNAL_TYPES_H */

include/uapi/asm-generic/signal-defs.h

+3 −0
Original line number Diff line number Diff line
@@ -20,6 +20,8 @@ 
 * so this bit allows flag bit support to be detected from userspace while

 * allowing an old kernel to be distinguished from a kernel that supports every

 * flag bit.

 * SA_EXPOSE_TAGBITS exposes an architecture-defined set of tag bits in

 * siginfo.si_addr.

 *

 * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single

 * Unix names RESETHAND and NODEFER respectively.
@@ -41,6 +43,7 @@ 
/* 0x00000100 used on sparc */

/* 0x00000200 used on sparc */

#define SA_UNSUPPORTED	0x00000400

#define SA_EXPOSE_TAGBITS	0x00000800

/* 0x00010000 used on mips */

/* 0x01000000 used on x86 */

/* 0x02000000 used on x86 */

kernel/signal.c

+24 −0
Original line number Diff line number Diff line
@@ -2524,6 +2524,26 @@ static int ptrace_signal(int signr, kernel_siginfo_t *info) 
	return signr;

}



static void hide_si_addr_tag_bits(struct ksignal *ksig)

{

	switch (siginfo_layout(ksig->sig, ksig->info.si_code)) {

	case SIL_FAULT:

	case SIL_FAULT_MCEERR:

	case SIL_FAULT_BNDERR:

	case SIL_FAULT_PKUERR:

		ksig->info.si_addr = arch_untagged_si_addr(

			ksig->info.si_addr, ksig->sig, ksig->info.si_code);

		break;

	case SIL_KILL:

	case SIL_TIMER:

	case SIL_POLL:

	case SIL_CHLD:

	case SIL_RT:

	case SIL_SYS:

		break;

	}

}



bool get_signal(struct ksignal *ksig)

{

	struct sighand_struct *sighand = current->sighand;
@@ -2761,6 +2781,10 @@ relock: 
	spin_unlock_irq(&sighand->siglock);



	ksig->sig = signr;



	if (!(ksig->ka.sa.sa_flags & SA_EXPOSE_TAGBITS))

		hide_si_addr_tag_bits(ksig);



	return ksig->sig > 0;

}

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