Re: Patch "signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP" has been added to the 4.15-stable tree

[ebiederm@xmission.com (Eric W. Biederman)]

<gregkh@linuxfoundation.org> writes:

> This is a note to let you know that I've just added the patch titled
>
>     signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP
>
> to the 4.15-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
>      signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch
> and it can be found in the queue-4.15 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

The patch is a noop functionality wise so I don't see the point of
backporting it to stable.

Eric

> From foo@baz Mon Apr  9 10:16:32 CEST 2018
> From: "Eric W. Biederman" <ebiederm@xmission.com>
> Date: Sat, 19 Aug 2017 15:26:01 -0500
> Subject: signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP
>
> From: "Eric W. Biederman" <ebiederm@xmission.com>
>
>
> [ Upstream commit cf4674c46c66e45f238f8f7e81af2a444b970c0a ]
>
> 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>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/powerpc/include/uapi/asm/siginfo.h |   15 +++++++++++++++
>  arch/powerpc/kernel/traps.c             |   10 +++++-----
>  2 files changed, 20 insertions(+), 5 deletions(-)
>
> --- a/arch/powerpc/include/uapi/asm/siginfo.h
> +++ b/arch/powerpc/include/uapi/asm/siginfo.h
> @@ -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 */
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -917,7 +917,7 @@ void unknown_exception(struct pt_regs *r
>  	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 p
>  
>  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
>  	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(stru
>  		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;
>  	}
>  }
>
>
> Patches currently in stable-queue which might be from ebiederm@xmission.com are
>
> queue-4.15/signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch
> queue-4.15/signal-arm-document-conflicts-with-si_user-and-sigfpe.patch
> queue-4.15/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch