From: Kees Cook <keescook@chromium.org>
To: YiFei Zhu <yifeifz2@illinois.edu>
Cc: Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Tycho Andersen <tycho@tycho.pizza>,
Andy Lutomirski <luto@amacapital.net>,
Will Drewry <wad@chromium.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Tobin Feldman-Fitzthum <tobin@ibm.com>,
Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
Valentin Rothberg <vrothber@redhat.com>,
Hubertus Franke <frankeh@us.ibm.com>,
Jack Chen <jianyan2@illinois.edu>,
Josep Torrellas <torrella@illinois.edu>,
Tianyin Xu <tyxu@illinois.edu>,
bpf@vger.kernel.org, containers@lists.linux-foundation.org,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 4/6] seccomp: Emulate basic filters for constant action results
Date: Wed, 23 Sep 2020 16:29:21 -0700 [thread overview]
Message-ID: <20200923232923.3142503-5-keescook@chromium.org> (raw)
In-Reply-To: <20200923232923.3142503-1-keescook@chromium.org>
This emulates absolutely the most basic seccomp filters to figure out
if they will always give the same results for a given arch/nr combo.
Nearly all seccomp filters are built from the following ops:
BPF_LD | BPF_W | BPF_ABS
BPF_JMP | BPF_JEQ | BPF_K
BPF_JMP | BPF_JGE | BPF_K
BPF_JMP | BPF_JGT | BPF_K
BPF_JMP | BPF_JSET | BPF_K
BPF_JMP | BPF_JA
BPF_RET | BPF_K
These are now emulated to check for accesses beyond seccomp_data::arch
or unknown instructions.
Not yet implemented are:
BPF_ALU | BPF_AND (generated by libseccomp and Chrome)
Suggested-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/lkml/CAG48ez1p=dR_2ikKq=xVxkoGg0fYpTBpkhJSv1w-6BG=76PAvw@mail.gmail.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
---
kernel/seccomp.c | 82 ++++++++++++++++++++++++++++++++++++++++++++---
net/core/filter.c | 3 +-
2 files changed, 79 insertions(+), 6 deletions(-)
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 111a238bc532..9921f6f39d12 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -610,7 +610,12 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
{
struct seccomp_filter *sfilter;
int ret;
- const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE);
+ const bool save_orig =
+#if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH)
+ true;
+#else
+ false;
+#endif
if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
return ERR_PTR(-EINVAL);
@@ -690,11 +695,78 @@ static inline bool sd_touched(pte_t *ptep)
* This approach could also be used to test for access to sd->arch too,
* if we wanted to warn about compat-unsafe filters.
*/
-static inline bool seccomp_filter_action_is_constant(struct bpf_prog *prog,
- struct seccomp_data *sd,
- u32 *action)
+static bool seccomp_filter_action_is_constant(struct bpf_prog *prog,
+ struct seccomp_data *sd,
+ u32 *action)
{
- /* No evaluation implementation yet. */
+ struct sock_fprog_kern *fprog = prog->orig_prog;
+ unsigned int insns;
+ unsigned int reg_value = 0;
+ unsigned int pc;
+ bool op_res;
+
+ if (WARN_ON_ONCE(!fprog))
+ return false;
+
+ insns = bpf_classic_proglen(fprog);
+ for (pc = 0; pc < insns; pc++) {
+ struct sock_filter *insn = &fprog->filter[pc];
+ u16 code = insn->code;
+ u32 k = insn->k;
+
+ switch (code) {
+ case BPF_LD | BPF_W | BPF_ABS:
+ switch (k) {
+ case offsetof(struct seccomp_data, nr):
+ reg_value = sd->nr;
+ break;
+ case offsetof(struct seccomp_data, arch):
+ reg_value = sd->arch;
+ break;
+ default:
+ /* can't optimize (non-constant value load) */
+ return false;
+ }
+ break;
+ case BPF_RET | BPF_K:
+ *action = insn->k;
+ /* success: reached return with constant values only */
+ return true;
+ case BPF_JMP | BPF_JA:
+ pc += insn->k;
+ break;
+ case BPF_JMP | BPF_JEQ | BPF_K:
+ case BPF_JMP | BPF_JGE | BPF_K:
+ case BPF_JMP | BPF_JGT | BPF_K:
+ case BPF_JMP | BPF_JSET | BPF_K:
+ switch (BPF_OP(code)) {
+ case BPF_JEQ:
+ op_res = reg_value == k;
+ break;
+ case BPF_JGE:
+ op_res = reg_value >= k;
+ break;
+ case BPF_JGT:
+ op_res = reg_value > k;
+ break;
+ case BPF_JSET:
+ op_res = !!(reg_value & k);
+ break;
+ default:
+ /* can't optimize (unknown jump) */
+ return false;
+ }
+
+ pc += op_res ? insn->jt : insn->jf;
+ break;
+ default:
+ /* can't optimize (unknown insn) */
+ return false;
+ }
+ }
+
+ /* ran off the end of the filter?! */
+ WARN_ON(1);
return false;
}
diff --git a/net/core/filter.c b/net/core/filter.c
index b2df52086445..cb1bdb0bfe87 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1145,7 +1145,7 @@ static int bpf_prog_store_orig_filter(struct bpf_prog *fp,
return 0;
}
-static void bpf_release_orig_filter(struct bpf_prog *fp)
+void bpf_release_orig_filter(struct bpf_prog *fp)
{
struct sock_fprog_kern *fprog = fp->orig_prog;
@@ -1154,6 +1154,7 @@ static void bpf_release_orig_filter(struct bpf_prog *fp)
kfree(fprog);
}
}
+EXPORT_SYMBOL_GPL(bpf_release_orig_filter);
static void __bpf_prog_release(struct bpf_prog *prog)
{
--
2.25.1
next prev parent reply other threads:[~2020-09-23 23:36 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 23:29 [PATCH v1 0/6] seccomp: Implement constant action bitmaps Kees Cook
2020-09-23 23:29 ` [PATCH 1/6] seccomp: Introduce SECCOMP_PIN_ARCHITECTURE Kees Cook
2020-09-24 0:41 ` Jann Horn
2020-09-24 7:11 ` Kees Cook
2020-09-23 23:29 ` [PATCH 2/6] x86: Enable seccomp architecture tracking Kees Cook
2020-09-24 0:45 ` Jann Horn
2020-09-24 7:12 ` Kees Cook
2020-09-23 23:29 ` [PATCH 3/6] seccomp: Implement constant action bitmaps Kees Cook
2020-09-24 0:25 ` Jann Horn
2020-09-24 7:36 ` Kees Cook
2020-09-24 8:07 ` YiFei Zhu
2020-09-24 8:15 ` Kees Cook
2020-09-24 8:22 ` YiFei Zhu
2020-09-24 12:28 ` Jann Horn
2020-09-24 12:37 ` David Laight
2020-09-24 12:56 ` Jann Horn
[not found] ` <DM6PR11MB271492D0565E91475D949F5DEF390@DM6PR11MB2714.namprd11.prod.outlook.com>
2020-09-24 0:36 ` YiFei Zhu
2020-09-24 7:38 ` Kees Cook
2020-09-24 7:51 ` YiFei Zhu
2020-09-23 23:29 ` Kees Cook [this message]
2020-09-23 23:47 ` [PATCH 4/6] seccomp: Emulate basic filters for constant action results Jann Horn
2020-09-24 7:46 ` Kees Cook
2020-09-24 15:28 ` Paul Moore
2020-09-24 19:52 ` Kees Cook
2020-09-24 20:46 ` Paul Moore
2020-09-24 21:35 ` Kees Cook
2020-09-23 23:29 ` [PATCH 5/6] selftests/seccomp: Compare bitmap vs filter overhead Kees Cook
2020-09-23 23:29 ` [PATCH 6/6] [DEBUG] seccomp: Report bitmap coverage ranges Kees Cook
2020-09-24 13:40 ` [PATCH v1 0/6] seccomp: Implement constant action bitmaps Rasmus Villemoes
2020-09-24 13:58 ` YiFei Zhu
2020-09-25 5:56 ` Rasmus Villemoes
2020-09-25 7:07 ` YiFei Zhu
2020-09-26 18:11 ` YiFei Zhu
2020-09-28 20:04 ` Kees Cook
2020-09-28 20:16 ` YiFei Zhu
2020-09-24 14:05 ` Jann Horn
2020-09-24 18:57 ` Andrea Arcangeli
2020-09-24 19:18 ` Jann Horn
[not found] ` <9dbe8e3bbdad43a1872202ff38c34ca2@DM5PR11MB1692.namprd11.prod.outlook.com>
2020-09-24 19:48 ` Tianyin Xu
2020-09-24 20:00 ` Kees Cook
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