Architecture must select HAVE_SECCOMP_FILTER_JIT and implement
seccomp_jit_compile() and seccomp_jit_free() if they intend to support
jitted seccomp filters.
Accessors to struct seccomp_filter fields are provided in
<linux/seccomp.h> to be used by the JIT code. With this, the 'struct
seccomp_filter' structure can stay opaque when outside
kernel/seccomp.c.
In a way similar to the net BPF, the jit compilation code is expected
to updates struct seccomp_filter.bpf_func pointer (using the correct
accessor) to the generated code.
Signed-off-by: Nicolas Schichan <nschic...@freebox.fr>
---
arch/Kconfig | 14 ++++++++++++++
include/linux/seccomp.h | 18 ++++++++++++++++++
kernel/seccomp.c | 33 ++++++++++++++++++++++++++++++++-
3 files changed, 64 insertions(+), 1 deletion(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 1455579..370bc52 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -332,6 +332,10 @@ config HAVE_ARCH_SECCOMP_FILTER
- secure_computing return value is checked and a return value of -1
results in the system call being skipped immediately.
+# Used by archs to tell that they support SECCOMP_FILTER_JIT
+config HAVE_SECCOMP_FILTER_JIT
+ bool
+
config SECCOMP_FILTER
def_bool y
depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
@@ -342,6 +346,16 @@ config SECCOMP_FILTER
See Documentation/prctl/seccomp_filter.txt for details.
+config SECCOMP_FILTER_JIT
+ bool "enable Seccomp filter Just In Time compiler"
+ depends on HAVE_SECCOMP_FILTER_JIT && BPF_JIT && SECCOMP_FILTER
+ help
+ Seccomp syscall filtering capabilities are normally handled
+ by an interpreter. This option allows kernel to generate a native
+ code when filter is loaded in memory. This should speedup
+ syscall filtering. Note : Admin should enable this feature
+ changing /proc/sys/net/core/bpf_jit_enable
+
config HAVE_CONTEXT_TRACKING
bool
help
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 6f19cfd..2793607 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -47,6 +47,24 @@ static inline int seccomp_mode(struct seccomp *s)
return s->mode;
}
+#ifdef CONFIG_SECCOMP_FILTER_JIT
+extern void seccomp_jit_compile(struct seccomp_filter *fp);
+extern void seccomp_jit_free(struct seccomp_filter *fp);
+
+/*
+ * accessors used by seccomp JIT code to avoid having to declare the
+ * seccomp_filter struct here.
+ */
+unsigned short seccomp_filter_get_len(struct seccomp_filter *fp);
+struct sock_filter *seccomp_filter_get_insns(struct seccomp_filter *fp);
+void seccomp_filter_set_bpf_func(struct seccomp_filter *fp, void *func);
+void *seccomp_filter_get_bpf_func(struct seccomp_filter *fp);
+
+#else
+static inline void seccomp_jit_compile(struct seccomp_filter *fp) { }
+static inline void seccomp_jit_free(struct seccomp_filter *fp) { }
+#endif
+
#else /* CONFIG_SECCOMP */
#include <linux/errno.h>
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index b7a1004..2377414 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -39,6 +39,8 @@
* is only needed for handling filters shared across tasks.
* @prev: points to a previously installed, or inherited, filter
* @len: the number of instructions in the program
+ * @bpf_func: points to either sk_run_filter or the code generated
+ * by the BPF JIT.
* @insns: the BPF program instructions to evaluate
*
* seccomp_filter objects are organized in a tree linked via the @prev
@@ -55,6 +57,8 @@ struct seccomp_filter {
atomic_t usage;
struct seccomp_filter *prev;
unsigned short len; /* Instruction count */
+ unsigned int (*bpf_func)(const struct sk_buff *skb,
+ const struct sock_filter *filter);
struct sock_filter insns[];
};
@@ -213,7 +217,7 @@ static u32 seccomp_run_filters(int syscall)
* value always takes priority (ignoring the DATA).
*/
for (f = current->seccomp.filter; f; f = f->prev) {
- u32 cur_ret = sk_run_filter(NULL, f->insns);
+ u32 cur_ret = f->bpf_func(NULL, f->insns);
if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
ret = cur_ret;
}
@@ -275,6 +279,9 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
if (ret)
goto fail;
+ filter->bpf_func = sk_run_filter;
+ seccomp_jit_compile(filter);
+
/*
* If there is an existing filter, make it the prev and don't drop its
* task reference.
@@ -332,10 +339,34 @@ void put_seccomp_filter(struct task_struct *tsk)
while (orig && atomic_dec_and_test(&orig->usage)) {
struct seccomp_filter *freeme = orig;
orig = orig->prev;
+ seccomp_jit_free(freeme);
kfree(freeme);
}
}
+/*
+ * seccomp filter accessors for JIT code.
+ */
+unsigned short seccomp_filter_get_len(struct seccomp_filter *fp)
+{
+ return fp->len;
+}
+
+struct sock_filter *seccomp_filter_get_insns(struct seccomp_filter *fp)
+{
+ return fp->insns;
+}
+
+void seccomp_filter_set_bpf_func(struct seccomp_filter *fp, void *func)
+{
+ fp->bpf_func = func;
+}
+
+void *seccomp_filter_get_bpf_func(struct seccomp_filter *fp)
+{
+ return fp->bpf_func;
+}
+
/**
* seccomp_send_sigsys - signals the task to allow in-process syscall emulation
* @syscall: syscall number to send to userland
--
1.7.10.4
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