lkml.org 
[lkml]   [2018]   [Dec]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[PATCH 3.16 296/328] ARC: clone syscall to setp r25 as thread pointer
    3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Vineet Gupta <vgupta@synopsys.com>

    commit c58a584f05e35d1d4342923cd7aac07d9c3d3d16 upstream.

    Per ARC TLS ABI, r25 is designated TP (thread pointer register).
    However so far kernel didn't do any special treatment, like setting up
    usermode r25, even for CLONE_SETTLS. We instead relied on libc runtime
    to do this, in say clone libc wrapper [1]. This was deliberate to keep
    kernel ABI agnostic (userspace could potentially change TP, specially
    for different ARC ISA say ARCompact vs. ARCv2 with different spare
    registers etc)

    However userspace setting up r25, after clone syscall opens a race, if
    child is not scheduled and gets a signal instead. It starts off in
    userspace not in clone but in a signal handler and anything TP sepcific
    there such as pthread_self() fails which showed up with uClibc
    testsuite nptl/tst-kill6 [2]

    Fix this by having kernel populate r25 to TP value. So this locks in
    ABI, but it was not going to change anyways, and fwiw is same for both
    ARCompact (arc700 core) and ARCvs (HS3x cores)

    [1] https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/sysdeps/linux/arc/clone.S
    [2] https://github.com/wbx-github/uclibc-ng-test/blob/master/test/nptl/tst-kill6.c

    Fixes: ARC STAR 9001378481
    Reported-by: Nikita Sobolev <sobolev@synopsys.com>
    Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/arc/kernel/process.c | 20 ++++++++++++++++++++
    1 file changed, 20 insertions(+)

    --- a/arch/arc/kernel/process.c
    +++ b/arch/arc/kernel/process.c
    @@ -147,6 +147,26 @@ int copy_thread(unsigned long clone_flag
    task_thread_info(current)->thr_ptr;
    }

    +
    + /*
    + * setup usermode thread pointer #1:
    + * when child is picked by scheduler, __switch_to() uses @c_callee to
    + * populate usermode callee regs: this works (despite being in a kernel
    + * function) since special return path for child @ret_from_fork()
    + * ensures those regs are not clobbered all the way to RTIE to usermode
    + */
    + c_callee->r25 = task_thread_info(p)->thr_ptr;
    +
    +#ifdef CONFIG_ARC_CURR_IN_REG
    + /*
    + * setup usermode thread pointer #2:
    + * however for this special use of r25 in kernel, __switch_to() sets
    + * r25 for kernel needs and only in the final return path is usermode
    + * r25 setup, from pt_regs->user_r25. So set that up as well
    + */
    + c_regs->user_r25 = c_callee->r25;
    +#endif
    +
    return 0;
    }

    \
     
     \ /
      Last update: 2018-12-09 23:04    [W:4.082 / U:0.068 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site