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    Subject[PATCH v15 11/13] ptrace,seccomp: Add PTRACE_SECCOMP support
    Date
    This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP,
    and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE.

    When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the
    tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that
    results in a BPF program returning SECCOMP_RET_TRACE. The 16-bit
    SECCOMP_RET_DATA mask of the BPF program return value will be passed as
    the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG.

    If the subordinate process is not using seccomp filter, then no
    system call notifications will occur even if the option is specified.

    If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE
    is returned, the system call will not be executed and an -ENOSYS errno
    will be returned to userspace.

    This change adds a dependency on the system call slow path. Any future
    efforts to use the system call fast path for seccomp filter will need to
    address this restriction.

    v15: - add audit support for non-zero return codes
    - clean up style (indan@nul.nu)
    v14: - rebase/nochanges
    v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
    (Brings back a change to ptrace.c and the masks.)
    v12: - rebase to linux-next
    - use ptrace_event and update arch/Kconfig to mention slow-path dependency
    - drop all tracehook changes and inclusion (oleg@redhat.com)
    v11: - invert the logic to just make it a PTRACE_SYSCALL accelerator
    (indan@nul.nu)
    v10: - moved to PTRACE_O_SECCOMP / PT_TRACE_SECCOMP
    v9: - n/a
    v8: - guarded PTRACE_SECCOMP use with an ifdef
    v7: - introduced

    Signed-off-by: Will Drewry <wad@chromium.org>
    ---
    arch/Kconfig | 11 ++++++-----
    include/linux/ptrace.h | 7 +++++--
    include/linux/seccomp.h | 1 +
    kernel/ptrace.c | 3 +++
    kernel/seccomp.c | 13 +++++++++++--
    5 files changed, 26 insertions(+), 9 deletions(-)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index d92a78e..3f8132c 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -202,15 +202,16 @@ config HAVE_CMPXCHG_DOUBLE
    config HAVE_ARCH_SECCOMP_FILTER
    bool
    help
    - This symbol should be selected by an architecure if it provides:
    - asm/syscall.h:
    + An arch should select this symbol if it provides all of these things:
    - syscall_get_arch()
    - syscall_get_arguments()
    - syscall_rollback()
    - syscall_set_return_value()
    - SIGSYS siginfo_t support must be implemented.
    - __secure_computing_int()/secure_computing()'s return value must be
    - checked, with -1 resulting in the syscall being skipped.
    + - SIGSYS siginfo_t support
    + - uses __secure_computing_int() or secure_computing()
    + - secure_computing is called from a ptrace_event()-safe context
    + - secure_computing return value is checked and a return value of -1
    + results in the system call being skipped immediately.

    config SECCOMP_FILTER
    def_bool y
    diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
    index c2f1f6a..84b3418 100644
    --- a/include/linux/ptrace.h
    +++ b/include/linux/ptrace.h
    @@ -62,8 +62,9 @@
    #define PTRACE_O_TRACEEXEC 0x00000010
    #define PTRACE_O_TRACEVFORKDONE 0x00000020
    #define PTRACE_O_TRACEEXIT 0x00000040
    +#define PTRACE_O_TRACESECCOMP 0x00000080

    -#define PTRACE_O_MASK 0x0000007f
    +#define PTRACE_O_MASK 0x000000ff

    /* Wait extended result codes for the above trace options. */
    #define PTRACE_EVENT_FORK 1
    @@ -73,6 +74,7 @@
    #define PTRACE_EVENT_VFORK_DONE 5
    #define PTRACE_EVENT_EXIT 6
    #define PTRACE_EVENT_STOP 7
    +#define PTRACE_EVENT_SECCOMP 8

    #include <asm/ptrace.h>

    @@ -101,8 +103,9 @@
    #define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
    #define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
    #define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
    +#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)

    -#define PT_TRACE_MASK 0x000003f4
    +#define PT_TRACE_MASK 0x00000ff4

    /* single stepping state bits (used on ARM and PA-RISC) */
    #define PT_SINGLESTEP_BIT 31
    diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
    index a5078fb..306733e 100644
    --- a/include/linux/seccomp.h
    +++ b/include/linux/seccomp.h
    @@ -21,6 +21,7 @@
    #define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
    #define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
    #define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
    +#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
    #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */

    /* Masks for the return value sections. */
    diff --git a/kernel/ptrace.c b/kernel/ptrace.c
    index 00ab2ca..8cf6da1 100644
    --- a/kernel/ptrace.c
    +++ b/kernel/ptrace.c
    @@ -551,6 +551,9 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
    if (data & PTRACE_O_TRACEEXIT)
    child->ptrace |= PT_TRACE_EXIT;

    + if (data & PTRACE_O_TRACESECCOMP)
    + child->ptrace |= PT_TRACE_SECCOMP;
    +
    return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
    }

    diff --git a/kernel/seccomp.c b/kernel/seccomp.c
    index fb3b993..725e83e 100644
    --- a/kernel/seccomp.c
    +++ b/kernel/seccomp.c
    @@ -17,13 +17,13 @@
    #include <linux/audit.h>
    #include <linux/compat.h>
    #include <linux/filter.h>
    +#include <linux/ptrace.h>
    #include <linux/sched.h>
    #include <linux/seccomp.h>
    #include <linux/security.h>
    #include <linux/slab.h>
    #include <linux/uaccess.h>

    -#include <linux/tracehook.h>
    #include <asm/syscall.h>

    /* #define SECCOMP_DEBUG 1 */
    @@ -398,7 +398,7 @@ int __secure_computing_int(int this_syscall)
    case SECCOMP_MODE_FILTER:
    ret = seccomp_run_filters(this_syscall);
    data = ret & SECCOMP_RET_DATA;
    - switch (code & SECCOMP_RET_ACTION) {
    + switch (ret & SECCOMP_RET_ACTION) {
    case SECCOMP_RET_ERRNO:
    /* Set the low-order 16-bits as a errno. */
    syscall_set_return_value(current, task_pt_regs(current),
    @@ -410,6 +410,15 @@ int __secure_computing_int(int this_syscall)
    /* Let the filter pass back 16 bits of data. */
    seccomp_send_sigsys(this_syscall, data);
    goto skip;
    + case SECCOMP_RET_TRACE:
    + /* Skip these calls if there is no tracer. */
    + if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP))
    + goto skip;
    + /* Allow the BPF to provide the event message */
    + ptrace_event(PTRACE_EVENT_SECCOMP, data);
    + if (fatal_signal_pending(current))
    + break;
    + return 0;
    case SECCOMP_RET_ALLOW:
    return 0;
    case SECCOMP_RET_KILL:
    --
    1.7.5.4


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