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Subject[PATCH v14 10/13] 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 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.

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 | 20 +++++++++++++++-----
5 files changed, 30 insertions(+), 12 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 e6d4b56..f4c1774 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/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 140490a..ddacc68 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 */
@@ -389,14 +389,24 @@ 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


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