[PATCH v12 10/13] ptrace,seccomp: Add PTRACE_SECCOMP support
From: Will Drewry <wad@chromium.org>
Date: 2012-02-29 23:55:11
Also in:
linux-arch, lkml
Subsystem:
ptrace support, secure computing, the rest · Maintainers:
Oleg Nesterov, Kees Cook, Linus Torvalds
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 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 attached tracer 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.
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 | 5 ++++-
include/linux/seccomp.h | 1 +
kernel/seccomp.c | 20 +++++++++++++++-----
4 files changed, 26 insertions(+), 11 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 6908bf6..beb1507 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig@@ -236,15 +236,16 @@ config ARCH_WANT_OLD_COMPAT_IPC 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 5c71962..597e4fd 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h@@ -58,6 +58,7 @@ #define PTRACE_EVENT_EXEC 4 #define PTRACE_EVENT_VFORK_DONE 5 #define PTRACE_EVENT_EXIT 6 +#define PTRACE_EVENT_SECCOMP 7 /* Extended result codes which enabled by means other than options. */ #define PTRACE_EVENT_STOP 128
@@ -69,8 +70,9 @@ #define PTRACE_O_TRACEEXEC (1 << PTRACE_EVENT_EXEC) #define PTRACE_O_TRACEVFORKDONE (1 << PTRACE_EVENT_VFORK_DONE) #define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT) +#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP) -#define PTRACE_O_MASK 0x0000007f +#define PTRACE_O_MASK 0x000000ff #include <asm/ptrace.h>
@@ -98,6 +100,7 @@ #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) /* 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 3fe48fd..e183598 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 0x00020000U /* disallow and force a SIGSYS */ #define SECCOMP_RET_ERRNO 0x00030000U /* returns an errno */ +#define SECCOMP_RET_TRACE 0x7ffe0000U /* pass to a tracer or disallow */ #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */ /* Masks for the return value sections. */
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 10c6077..1064327 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 */
@@ -346,14 +346,24 @@ int __secure_computing_int(int this_syscall) -(action & SECCOMP_RET_DATA), 0); return -1; - case SECCOMP_RET_TRAP: { - int reason_code = action & SECCOMP_RET_DATA; + case SECCOMP_RET_TRAP: /* Show the handler the original registers. */ syscall_rollback(current, task_pt_regs(current)); /* Let the filter pass back 16 bits of data. */ - seccomp_send_sigsys(this_syscall, reason_code); + seccomp_send_sigsys(this_syscall, + action & SECCOMP_RET_DATA); return -1; - } + case SECCOMP_RET_TRACE: + /* Skip these calls if there is no tracer. */ + if (!ptrace_event_enabled(current, + PTRACE_EVENT_SECCOMP)) + return -1; + /* Allow the BPF to provide the event message */ + ptrace_event(PTRACE_EVENT_SECCOMP, + action & SECCOMP_RET_DATA); + if (fatal_signal_pending(current)) + break; + return 0; case SECCOMP_RET_ALLOW: return 0; case SECCOMP_RET_KILL:
--
1.7.5.4