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Subject[PATCH v9 5/8] seccomp: Add SECCOMP_RET_TRAP
Date
Adds a new return value to seccomp filters that triggers a SIGILL to be
delivered with the new ILL_SECCOMP si_code.

This allows in-process system call emulation, including just specifying
an errno or cleanly dumping core, rather than just dying. It also
avoids interfering with normal debugger operation (injecting SIGTRAPs).

v9: - changes to SIGILL (markus@chromium.org)
v8: - clean up based on changes to dependent patches
v7: - introduction

Signed-off-by: Will Drewry <wad@chromium.org>
---
arch/Kconfig | 8 ++++----
include/asm-generic/siginfo.h | 3 ++-
include/linux/seccomp.h | 1 +
kernel/seccomp.c | 20 ++++++++++++++++++++
4 files changed, 27 insertions(+), 5 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 3f3052b..a01c151 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -203,10 +203,10 @@ config HAVE_ARCH_SECCOMP_FILTER
bool
help
This symbol should be selected by an architecure if it provides
- asm/syscall.h, specifically syscall_get_arguments() and
- syscall_set_return_value(). Additionally, its system call
- entry path must respect a return value of -1 from
- __secure_computing_int() and/or secure_computing().
+ asm/syscall.h, specifically syscall_get_arguments(),
+ syscall_set_return_value(), and syscall_rollback().
+ Additionally, its system call entry path must respect a return
+ value of -1 from __secure_computing_int() and/or secure_computing().

config SECCOMP_FILTER
def_bool y
diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h
index 0dd4e87..e565662 100644
--- a/include/asm-generic/siginfo.h
+++ b/include/asm-generic/siginfo.h
@@ -166,7 +166,8 @@ typedef struct siginfo {
#define ILL_PRVREG (__SI_FAULT|6) /* privileged register */
#define ILL_COPROC (__SI_FAULT|7) /* coprocessor error */
#define ILL_BADSTK (__SI_FAULT|8) /* internal stack error */
-#define NSIGILL 8
+#define ILL_SECCOMP (__SI_FAULT|9) /* illegal syscall via seccomp */
+#define NSIGILL 9

/*
* SIGFPE si_codes
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 879ece2..1be562f 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -19,6 +19,7 @@
* selects the least permissive choice.
*/
#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
+#define SECCOMP_RET_TRAP 0x00020000U /* disallow and send sigtrap */
#define SECCOMP_RET_ERRNO 0x00030000U /* returns an errno */
#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 55d000d..a7b6510 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -290,6 +290,21 @@ void copy_seccomp(struct seccomp *child,
child->mode = prev->mode;
child->filter = get_seccomp_filter(prev->filter);
}
+
+/**
+ * seccomp_send_sigill - signals the task to allow in-process syscall emulation
+ *
+ * Forces a SIGILL with si_code of ILL_SECCOMP.
+ */
+static void seccomp_send_sigill(void)
+{
+ struct siginfo info;
+ memset(&info, 0, sizeof(info));
+ info.si_signo = SIGILL;
+ info.si_code = ILL_SECCOMP;
+ info.si_addr = (void __user *)KSTK_EIP(current);
+ force_sig_info(SIGILL, &info, current);
+}
#endif /* CONFIG_SECCOMP_FILTER */

/*
@@ -343,6 +358,11 @@ int __secure_computing_int(int this_syscall)
-(action & SECCOMP_RET_DATA),
0);
return -1;
+ case SECCOMP_RET_TRAP:
+ /* Show the handler the original registers. */
+ syscall_rollback(current, task_pt_regs(current));
+ seccomp_send_sigill();
+ return -1;
case SECCOMP_RET_ALLOW:
return 0;
case SECCOMP_RET_KILL:
--
1.7.5.4


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