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[RFC 4/5] seccomp: Allow arch code to provide seccomp_data

To: linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>, Will Drewry <wad@chromium.org>
Subject: [RFC 4/5] seccomp: Allow arch code to provide seccomp_data
From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 11 Jun 2014 13:23:01 -0700
Cc: Oleg Nesterov <oleg@redhat.com>, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-arch@vger.kernel.org, linux-security-module@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>
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Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---
 include/linux/seccomp.h |  2 +-
 kernel/seccomp.c        | 32 +++++++++++++++++++-------------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 8345fdc..4fc7a84 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -37,7 +37,7 @@ static inline int secure_computing(void)
 #define SECCOMP_PHASE1_OK      0
 #define SECCOMP_PHASE1_SKIP    1
 
-extern u32 seccomp_phase1(void);
+extern u32 seccomp_phase1(struct seccomp_data *sd);
 int seccomp_phase2(u32 phase1_result);
 #else
 extern void secure_computing_strict(int this_syscall);
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index dfdb38a..6848912 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -173,24 +173,27 @@ static int seccomp_check_filter(struct sock_filter 
*filter, unsigned int flen)
  *
  * Returns valid seccomp BPF response codes.
  */
-static u32 seccomp_run_filters(void)
+static u32 seccomp_run_filters(struct seccomp_data *sd)
 {
        struct seccomp_filter *f;
-       struct seccomp_data sd;
+       struct seccomp_data sd_local;
        u32 ret = SECCOMP_RET_ALLOW;
 
        /* Ensure unexpected behavior doesn't result in failing open. */
        if (WARN_ON(current->seccomp.filter == NULL))
                return SECCOMP_RET_KILL;
 
-       populate_seccomp_data(&sd);
+       if (!sd) {
+               populate_seccomp_data(&sd_local);
+               sd = &sd_local;
+       }
 
        /*
         * All filters in the list are evaluated and the lowest BPF return
         * value always takes priority (ignoring the DATA).
         */
        for (f = current->seccomp.filter; f; f = f->prev) {
-               u32 cur_ret = sk_run_filter_int_seccomp(&sd, f->insnsi);
+               u32 cur_ret = sk_run_filter_int_seccomp(sd, f->insnsi);
                if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
                        ret = cur_ret;
        }
@@ -406,7 +409,7 @@ void secure_computing_strict(int this_syscall)
 #else
 int __secure_computing(void)
 {
-       u32 phase1_result = seccomp_phase1();
+       u32 phase1_result = seccomp_phase1(NULL);
        if (likely(phase1_result == SECCOMP_PHASE1_OK))
                return 0;
        else if (likely(phase1_result == SECCOMP_PHASE1_SKIP))
@@ -416,22 +419,22 @@ int __secure_computing(void)
 }
 
 #ifdef CONFIG_SECCOMP_FILTER
-static u32 __seccomp_phase1_filter(int this_syscall, struct pt_regs *regs)
+static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd)
 {
-       u32 filter_ret = seccomp_run_filters();
+       u32 filter_ret = seccomp_run_filters(sd);
        int data = filter_ret & SECCOMP_RET_DATA;
        u32 action = filter_ret & SECCOMP_RET_ACTION;
 
        switch (action) {
        case SECCOMP_RET_ERRNO:
                /* Set the low-order 16-bits as a errno. */
-               syscall_set_return_value(current, regs,
+               syscall_set_return_value(current, task_pt_regs(current),
                                         -data, 0);
                goto skip;
 
        case SECCOMP_RET_TRAP:
                /* Show the handler the original registers. */
-               syscall_rollback(current, regs);
+               syscall_rollback(current, task_pt_regs(current));
                /* Let the filter pass back 16 bits of data. */
                seccomp_send_sigsys(this_syscall, data);
                goto skip;
@@ -458,11 +461,14 @@ skip:
 
 /**
  * seccomp_phase1() - run fast path seccomp checks on the current syscall
+ * @arg sd: The seccomp_data or NULL
  *
  * This only reads pt_regs via the syscall_xyz helpers.  The only change
  * it will make to pt_regs is via syscall_set_return_value, and it will
  * only do that if it returns SECCOMP_PHASE1_SKIP.
  *
+ * If sd is provided, it will not read pt_regs at all.
+ *
  * It may also call do_exit or force a signal; these actions must be
  * safe.
  *
@@ -476,11 +482,11 @@ skip:
  * If it returns anything else, then the return value should be passed
  * to seccomp_phase2 from a context in which ptrace hooks are safe.
  */
-u32 seccomp_phase1(void)
+u32 seccomp_phase1(struct seccomp_data *sd)
 {
        int mode = current->seccomp.mode;
-       struct pt_regs *regs = task_pt_regs(current);
-       int this_syscall = syscall_get_nr(current, regs);
+       int this_syscall = sd ? sd->nr :
+               syscall_get_nr(current, task_pt_regs(current));
 
        switch (mode) {
        case SECCOMP_MODE_STRICT:
@@ -488,7 +494,7 @@ u32 seccomp_phase1(void)
                return SECCOMP_PHASE1_OK;
 #ifdef CONFIG_SECCOMP_FILTER
        case SECCOMP_MODE_FILTER:
-               return __seccomp_phase1_filter(this_syscall, regs);
+               return __seccomp_phase1_filter(this_syscall, sd);
 #endif
        default:
                BUG();
-- 
1.9.3


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