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    SubjectRe: [PATCH 04/11] signal/parisc: Document a conflict with SI_USER with SIGFPE
    * Eric W. Biederman <ebiederm@xmission.com>:
    > 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 siginfo_layout will now return SIL_FAULT and the
    > appropriate fields will reliably be copied.
    >
    > This bug is 13 years old and parsic machines are no longer being built
    > so I don't know if it possible or worth fixing it. But it is at least
    > worth documenting this so other architectures don't make the same
    > mistake.


    I think we should fix it, even if we now break the ABI.

    It's about a "conditional trap" which needs to be handled by userspace.
    I doubt there is any Linux code out which is utilizing this
    parisc-specific trap.

    I'd suggest to add a new FPE trap si_code (e.g. FPE_CONDTRAP).
    While at it, maybe we should include the already existing FPE_MDAOVF
    from the frv architecture, so that arch/frv/include/uapi/asm/siginfo.h
    can go completely.

    Suggested patch is below.

    I'm willing to test the patch below on the parisc architecture for a few
    weeks. And it will break arch/x86/kernel/signal_compat.c which needs
    looking at then too.

    Thoughts?

    Helge



    [PATCH] parisc: Add FPE_CONDTRAP for conditional trap handling

    Posix and common sense requires that SI_USER not be a signal specific
    si_code. Thus add a new FPE_CONDTRAP si_code for conditional traps.

    Signed-off-by: Helge Deller <deller@gmx.de>

    diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
    index 8453724b8009..13702f0f5ba1 100644
    --- a/arch/parisc/kernel/traps.c
    +++ b/arch/parisc/kernel/traps.c
    @@ -627,9 +627,9 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
    on condition */
    if(user_mode(regs)){
    si.si_signo = SIGFPE;
    - /* Set to zero, and let the userspace app figure it out from
    - the insn pointed to by si_addr */
    - si.si_code = 0;
    + /* Let userspace app figure out from the insn pointed
    + * to by si_addr */
    + si.si_code = FPE_CONDTRAP;
    si.si_addr = (void __user *) regs->iaoq[0];
    force_sig_info(SIGFPE, &si, current);
    return;
    diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
    index e447283b8f52..2b759fe42142 100644
    --- a/include/uapi/asm-generic/siginfo.h
    +++ b/include/uapi/asm-generic/siginfo.h
    @@ -193,7 +193,9 @@ typedef struct siginfo {
    #define FPE_FLTRES 6 /* floating point inexact result */
    #define FPE_FLTINV 7 /* floating point invalid operation */
    #define FPE_FLTSUB 8 /* subscript out of range */
    -#define NSIGFPE 8
    +#define FPE_MDAOVF 9 /* media overflow */
    +#define FPE_CONDTRAP 10 /* trap on condition */
    +#define NSIGFPE 10

    /*
    * SIGSEGV si_codes
    \
     
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      Last update: 2018-01-14 23:26    [W:2.434 / U:0.228 seconds]
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