lkml.org 
[lkml]   [2016]   [Mar]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.2.y-ckt 56/98] parisc: Fix ptrace syscall number and return value modification
    Date
    4.2.8-ckt6 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Helge Deller <deller@gmx.de>

    commit 98e8b6c9ac9d1b1e9d1122dfa6783d5d566bb8f7 upstream.

    Mike Frysinger reported that his ptrace testcase showed strange
    behaviour on parisc: It was not possible to avoid a syscall and the
    return value of a syscall couldn't be changed.

    To modify a syscall number, we were missing to save the new syscall
    number to gr20 which is then picked up later in assembly again.

    The effect that the return value couldn't be changed is a side-effect of
    another bug in the assembly code. When a process is ptraced, userspace
    expects each syscall to report entrance and exit of a syscall. If a
    syscall number was given which doesn't exist, we jumped to the normal
    syscall exit code instead of informing userspace that the (non-existant)
    syscall exits. This unexpected behaviour confuses userspace and thus the
    bug was misinterpreted as if we can't change the return value.

    This patch fixes both problems and was tested on 64bit kernel with
    32bit userspace.

    Signed-off-by: Helge Deller <deller@gmx.de>
    Cc: Mike Frysinger <vapier@gentoo.org>
    Tested-by: Mike Frysinger <vapier@gentoo.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    arch/parisc/kernel/ptrace.c | 16 +++++++++++-----
    arch/parisc/kernel/syscall.S | 5 ++++-
    2 files changed, 15 insertions(+), 6 deletions(-)

    diff --git a/arch/parisc/kernel/ptrace.c b/arch/parisc/kernel/ptrace.c
    index 9585c81..ce0b2b4 100644
    --- a/arch/parisc/kernel/ptrace.c
    +++ b/arch/parisc/kernel/ptrace.c
    @@ -269,14 +269,19 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,

    long do_syscall_trace_enter(struct pt_regs *regs)
    {
    - long ret = 0;
    -
    /* Do the secure computing check first. */
    secure_computing_strict(regs->gr[20]);

    if (test_thread_flag(TIF_SYSCALL_TRACE) &&
    - tracehook_report_syscall_entry(regs))
    - ret = -1L;
    + tracehook_report_syscall_entry(regs)) {
    + /*
    + * Tracing decided this syscall should not happen or the
    + * debugger stored an invalid system call number. Skip
    + * the system call and the system call restart handling.
    + */
    + regs->gr[20] = -1UL;
    + goto out;
    + }

    #ifdef CONFIG_64BIT
    if (!is_compat_task())
    @@ -290,7 +295,8 @@ long do_syscall_trace_enter(struct pt_regs *regs)
    regs->gr[24] & 0xffffffff,
    regs->gr[23] & 0xffffffff);

    - return ret ? : regs->gr[20];
    +out:
    + return regs->gr[20];
    }

    void do_syscall_trace_exit(struct pt_regs *regs)
    diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
    index 0b8d26d..02cf40c 100644
    --- a/arch/parisc/kernel/syscall.S
    +++ b/arch/parisc/kernel/syscall.S
    @@ -343,7 +343,7 @@ tracesys_next:
    #endif

    comiclr,>>= __NR_Linux_syscalls, %r20, %r0
    - b,n .Lsyscall_nosys
    + b,n .Ltracesys_nosys

    LDREGX %r20(%r19), %r19

    @@ -359,6 +359,9 @@ tracesys_next:
    be 0(%sr7,%r19)
    ldo R%tracesys_exit(%r2),%r2

    +.Ltracesys_nosys:
    + ldo -ENOSYS(%r0),%r28 /* set errno */
    +
    /* Do *not* call this function on the gateway page, because it
    makes a direct call to syscall_trace. */

    --
    2.7.0
    \
     
     \ /
      Last update: 2016-03-16 01:21    [W:4.085 / U:0.076 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site