• Helge Deller's avatar
    parisc: Fix ptrace syscall number and return value modification · 59dc7ab2
    Helge Deller authored
    commit 98e8b6c9 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: default avatarHelge Deller <deller@gmx.de>
    Cc: Mike Frysinger <vapier@gentoo.org>
    Tested-by: default avatarMike Frysinger <vapier@gentoo.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    59dc7ab2
syscall.S 26 KB