lkml.org 
[lkml]   [2015]   [Jul]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[tip:x86/asm] x86/entry/64/compat: Fix bad fast syscall arg failure path
    Commit-ID:  5e99cb7c35ca0580da8e892f91c655d35ecf8798
    Gitweb: http://git.kernel.org/tip/5e99cb7c35ca0580da8e892f91c655d35ecf8798
    Author: Andy Lutomirski <luto@kernel.org>
    AuthorDate: Fri, 3 Jul 2015 12:44:19 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Tue, 7 Jul 2015 10:58:30 +0200

    x86/entry/64/compat: Fix bad fast syscall arg failure path

    If user code does SYSCALL32 or SYSENTER without a valid stack,
    then our attempt to determine the syscall args will result in a
    failed uaccess fault. Previously, we would try to recover by
    jumping to the syscall exit code, but we'd run the syscall exit
    work even though we never made it to the syscall entry work.

    Clean it up by treating the failure path as a non-syscall entry
    and exit pair.

    This fixes strace's output when running the syscall_arg_fault
    test. Without this fix, strace would get out of sync and would
    fail to associate syscall entries with syscall exits.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Denys Vlasenko <vda.linux@googlemail.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: paulmck@linux.vnet.ibm.com
    Link: http://lkml.kernel.org/r/903010762c07a3d67df914fea2da84b52b0f8f1d.1435952415.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/entry/entry_64.S | 2 +-
    arch/x86/entry/entry_64_compat.S | 35 +++++++++++++++++++++++++++++++++--
    2 files changed, 34 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
    index 3bb2c43..141a5d4 100644
    --- a/arch/x86/entry/entry_64.S
    +++ b/arch/x86/entry/entry_64.S
    @@ -613,7 +613,7 @@ ret_from_intr:
    testb $3, CS(%rsp)
    jz retint_kernel
    /* Interrupt came from user space */
    -retint_user:
    +GLOBAL(retint_user)
    GET_THREAD_INFO(%rcx)

    /* %rcx: thread info. Interrupts are off. */
    diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
    index b868cfc..e5ebdd9 100644
    --- a/arch/x86/entry/entry_64_compat.S
    +++ b/arch/x86/entry/entry_64_compat.S
    @@ -428,8 +428,39 @@ cstar_tracesys:
    END(entry_SYSCALL_compat)

    ia32_badarg:
    - ASM_CLAC
    - movq $-EFAULT, RAX(%rsp)
    + /*
    + * So far, we've entered kernel mode, set AC, turned on IRQs, and
    + * saved C regs except r8-r11. We haven't done any of the other
    + * standard entry work, though. We want to bail, but we shouldn't
    + * treat this as a syscall entry since we don't even know what the
    + * args are. Instead, treat this as a non-syscall entry, finish
    + * the entry work, and immediately exit after setting AX = -EFAULT.
    + *
    + * We're really just being polite here. Killing the task outright
    + * would be a reasonable action, too. Given that the only valid
    + * way to have gotten here is through the vDSO, and we already know
    + * that the stack pointer is bad, the task isn't going to survive
    + * for long no matter what we do.
    + */
    +
    + ASM_CLAC /* undo STAC */
    + movq $-EFAULT, RAX(%rsp) /* return -EFAULT if possible */
    +
    + /* Fill in the rest of pt_regs */
    + xorl %eax, %eax
    + movq %rax, R11(%rsp)
    + movq %rax, R10(%rsp)
    + movq %rax, R9(%rsp)
    + movq %rax, R8(%rsp)
    + SAVE_EXTRA_REGS
    +
    + /* Turn IRQs back off. */
    + DISABLE_INTERRUPTS(CLBR_NONE)
    + TRACE_IRQS_OFF
    +
    + /* And exit again. */
    + jmp retint_user
    +
    ia32_ret_from_sys_call:
    xorl %eax, %eax /* Do not leak kernel information */
    movq %rax, R11(%rsp)

    \
     
     \ /
      Last update: 2015-07-07 13:01    [W:3.097 / U:0.000 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site