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signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP 

Setting si_code to 0 results in a userspace seeing an si_code of 0.
This is the same si_code as SI_USER.  Posix and common sense requires
that SI_USER not be a signal specific si_code.  As such this use of 0
for the si_code is a pretty horribly broken ABI.

Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
value of __SI_KILL and now sees a value of SIL_KILL with the result
that uid and pid fields are copied and which might copying the si_addr
field by accident but certainly not by design.  Making this a very
flakey implementation.

Utilizing FPE_FIXME and TRAP_FIXME, siginfo_layout() will now return
SIL_FAULT and the appropriate fields will be reliably copied.

Possible ABI fixes includee:
- Send the signal without siginfo
- Don't generate a signal
- Possibly assign and use an appropriate si_code
- Don't handle cases which can't happen
Cc: Paul Mackerras <paulus@samba.org>
Cc: Kumar Gala <kumar.gala@freescale.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:  linuxppc-dev@lists.ozlabs.org
Ref: 9bad068c24d7 ("[PATCH] ppc32: support for e500 and 85xx")
Ref: 0ed70f6105ef ("PPC32: Provide proper siginfo information on various exceptions.")
History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-08-19 15:26:01 -05:00
parent b80328be53
commit cf4674c46c
2 changed files with 20 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
arch/powerpc/include/uapi/asm/siginfo.h
View File

@ -18,4 +18,19 @@
#undef NSIGTRAP
#define NSIGTRAP 4
/*
* SIGFPE si_codes
*/
#ifdef __KERNEL__
#define FPE_FIXME 0 /* Broken dup of SI_USER */
#endif /* __KERNEL__ */
/*
* SIGTRAP si_codes
*/
#ifdef __KERNEL__
#define TRAP_FIXME 0 /* Broken dup of SI_USER */
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_SIGINFO_H */

10
arch/powerpc/kernel/traps.c
View File

@ -917,7 +917,7 @@ void unknown_exception(struct pt_regs *regs)
printk("Bad trap at PC: %lx, SR: %lx, vector=%lx\n",
regs->nip, regs->msr, regs->trap);
_exception(SIGTRAP, regs, 0, 0);
_exception(SIGTRAP, regs, TRAP_FIXME, 0);
exception_exit(prev_state);
}
@ -939,7 +939,7 @@ bail:
void RunModeException(struct pt_regs *regs)
{
_exception(SIGTRAP, regs, 0, 0);
_exception(SIGTRAP, regs, TRAP_FIXME, 0);
}
void single_step_exception(struct pt_regs *regs)
@ -978,7 +978,7 @@ static void emulate_single_step(struct pt_regs *regs)
static inline int __parse_fpscr(unsigned long fpscr)
{
int ret = 0;
int ret = FPE_FIXME;
/* Invalid operation */
if ((fpscr & FPSCR_VE) && (fpscr & FPSCR_VX))
@ -1929,7 +1929,7 @@ void SPEFloatingPointException(struct pt_regs *regs)
extern int do_spe_mathemu(struct pt_regs *regs);
unsigned long spefscr;
int fpexc_mode;
int code = 0;
int code = FPE_FIXME;
int err;
flush_spe_to_thread(current);
@ -1998,7 +1998,7 @@ void SPEFloatingPointRoundException(struct pt_regs *regs)
printk(KERN_ERR "unrecognized spe instruction "
"in %s at %lx\n", current->comm, regs->nip);
} else {
_exception(SIGFPE, regs, 0, regs->nip);
_exception(SIGFPE, regs, FPE_FIXME, regs->nip);
return;
}
}