From 69772f509e084ec6bca12dbcdeeeff41b0103774 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Tue, 3 Dec 2024 20:47:53 -0800 Subject: [PATCH 1/5] bpf: Don't mark STACK_INVALID as STACK_MISC in mark_stack_slot_misc Inside mark_stack_slot_misc, we should not upgrade STACK_INVALID to STACK_MISC when allow_ptr_leaks is false, since invalid contents shouldn't be read unless the program has the relevant capabilities. The relaxation only makes sense when env->allow_ptr_leaks is true. However, such conversion in privileged mode becomes unnecessary, as invalid slots can be read without being upgraded to STACK_MISC. Currently, the condition is inverted (i.e. checking for true instead of false), simply remove it to restore correct behavior. Fixes: eaf18febd6eb ("bpf: preserve STACK_ZERO slots on partial reg spills") Acked-by: Andrii Nakryiko Reported-by: Tao Lyu Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241204044757.1483141-2-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2fd35465d650..f18aad339de8 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1202,14 +1202,17 @@ static bool is_spilled_scalar_reg64(const struct bpf_stack_state *stack) /* Mark stack slot as STACK_MISC, unless it is already STACK_INVALID, in which * case they are equivalent, or it's STACK_ZERO, in which case we preserve * more precise STACK_ZERO. - * Note, in uprivileged mode leaving STACK_INVALID is wrong, so we take - * env->allow_ptr_leaks into account and force STACK_MISC, if necessary. + * Regardless of allow_ptr_leaks setting (i.e., privileged or unprivileged + * mode), we won't promote STACK_INVALID to STACK_MISC. In privileged case it is + * unnecessary as both are considered equivalent when loading data and pruning, + * in case of unprivileged mode it will be incorrect to allow reads of invalid + * slots. */ static void mark_stack_slot_misc(struct bpf_verifier_env *env, u8 *stype) { if (*stype == STACK_ZERO) return; - if (env->allow_ptr_leaks && *stype == STACK_INVALID) + if (*stype == STACK_INVALID) return; *stype = STACK_MISC; } From b0e66977dc072906bb76555fb1a64261d7f63d0f Mon Sep 17 00:00:00 2001 From: Tao Lyu Date: Tue, 3 Dec 2024 20:47:54 -0800 Subject: [PATCH 2/5] bpf: Fix narrow scalar spill onto 64-bit spilled scalar slots When CAP_PERFMON and CAP_SYS_ADMIN (allow_ptr_leaks) are disabled, the verifier aims to reject partial overwrite on an 8-byte stack slot that contains a spilled pointer. However, in such a scenario, it rejects all partial stack overwrites as long as the targeted stack slot is a spilled register, because it does not check if the stack slot is a spilled pointer. Incomplete checks will result in the rejection of valid programs, which spill narrower scalar values onto scalar slots, as shown below. 0: R1=ctx() R10=fp0 ; asm volatile ( @ repro.bpf.c:679 0: (7a) *(u64 *)(r10 -8) = 1 ; R10=fp0 fp-8_w=1 1: (62) *(u32 *)(r10 -8) = 1 attempt to corrupt spilled pointer on stack processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0. Fix this by expanding the check to not consider spilled scalar registers when rejecting the write into the stack. Previous discussion on this patch is at link [0]. [0]: https://lore.kernel.org/bpf/20240403202409.2615469-1-tao.lyu@epfl.ch Fixes: ab125ed3ec1c ("bpf: fix check for attempt to corrupt spilled pointer") Acked-by: Eduard Zingerman Acked-by: Andrii Nakryiko Signed-off-by: Tao Lyu Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241204044757.1483141-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f18aad339de8..01fbef9576e0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4703,6 +4703,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env, */ if (!env->allow_ptr_leaks && is_spilled_reg(&state->stack[spi]) && + !is_spilled_scalar_reg(&state->stack[spi]) && size != BPF_REG_SIZE) { verbose(env, "attempt to corrupt spilled pointer on stack\n"); return -EACCES; From adfdd9c68566120debc622712888c4d084539081 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Tue, 3 Dec 2024 20:47:55 -0800 Subject: [PATCH 3/5] selftests/bpf: Introduce __caps_unpriv annotation for tests Add a __caps_unpriv annotation so that tests requiring specific capabilities while dropping the rest can conveniently specify them during selftest declaration instead of munging with capabilities at runtime from the testing binary. While at it, let us convert test_verifier_mtu to use this new support instead. Since we do not want to include linux/capability.h, we only defined the four main capabilities BPF subsystem deals with in bpf_misc.h for use in tests. If the user passes a CAP_SYS_NICE or anything else that's not defined in the header, capability parsing code will return a warning. Also reject strtol returning 0. CAP_CHOWN = 0 but we'll never need to use it, and strtol doesn't errno on failed conversion. Fail the test in such a case. The original diff for this idea is available at link [0]. [0]: https://lore.kernel.org/bpf/a1e48f5d9ae133e19adc6adf27e19d585e06bab4.camel@gmail.com Signed-off-by: Eduard Zingerman [ Kartikeya: rebase on bpf-next, add warn to parse_caps, convert test_verifier_mtu ] Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241204044757.1483141-4-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/prog_tests/verifier.c | 19 +------- tools/testing/selftests/bpf/progs/bpf_misc.h | 12 +++++ .../selftests/bpf/progs/verifier_mtu.c | 4 +- tools/testing/selftests/bpf/test_loader.c | 46 +++++++++++++++++++ 4 files changed, 62 insertions(+), 19 deletions(-) diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c index d9f65adb456b..3ee40ee9413a 100644 --- a/tools/testing/selftests/bpf/prog_tests/verifier.c +++ b/tools/testing/selftests/bpf/prog_tests/verifier.c @@ -225,24 +225,7 @@ void test_verifier_xdp(void) { RUN(verifier_xdp); } void test_verifier_xdp_direct_packet_access(void) { RUN(verifier_xdp_direct_packet_access); } void test_verifier_bits_iter(void) { RUN(verifier_bits_iter); } void test_verifier_lsm(void) { RUN(verifier_lsm); } - -void test_verifier_mtu(void) -{ - __u64 caps = 0; - int ret; - - /* In case CAP_BPF and CAP_PERFMON is not set */ - ret = cap_enable_effective(1ULL << CAP_BPF | 1ULL << CAP_NET_ADMIN, &caps); - if (!ASSERT_OK(ret, "set_cap_bpf_cap_net_admin")) - return; - ret = cap_disable_effective(1ULL << CAP_SYS_ADMIN | 1ULL << CAP_PERFMON, NULL); - if (!ASSERT_OK(ret, "disable_cap_sys_admin")) - goto restore_cap; - RUN(verifier_mtu); -restore_cap: - if (caps) - cap_enable_effective(caps, NULL); -} +void test_verifier_mtu(void) { RUN(verifier_mtu); } static int init_test_val_map(struct bpf_object *obj, char *map_name) { diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h index eccaf955e394..f45f4352feeb 100644 --- a/tools/testing/selftests/bpf/progs/bpf_misc.h +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h @@ -5,6 +5,10 @@ #define XSTR(s) STR(s) #define STR(s) #s +/* Expand a macro and then stringize the expansion */ +#define QUOTE(str) #str +#define EXPAND_QUOTE(str) QUOTE(str) + /* This set of attributes controls behavior of the * test_loader.c:test_loader__run_subtests(). * @@ -106,6 +110,7 @@ * __arch_* Specify on which architecture the test case should be tested. * Several __arch_* annotations could be specified at once. * When test case is not run on current arch it is marked as skipped. + * __caps_unpriv Specify the capabilities that should be set when running the test. */ #define __msg(msg) __attribute__((btf_decl_tag("comment:test_expect_msg=" XSTR(__COUNTER__) "=" msg))) #define __xlated(msg) __attribute__((btf_decl_tag("comment:test_expect_xlated=" XSTR(__COUNTER__) "=" msg))) @@ -129,6 +134,13 @@ #define __arch_x86_64 __arch("X86_64") #define __arch_arm64 __arch("ARM64") #define __arch_riscv64 __arch("RISCV64") +#define __caps_unpriv(caps) __attribute__((btf_decl_tag("comment:test_caps_unpriv=" EXPAND_QUOTE(caps)))) + +/* Define common capabilities tested using __caps_unpriv */ +#define CAP_NET_ADMIN 12 +#define CAP_SYS_ADMIN 21 +#define CAP_PERFMON 38 +#define CAP_BPF 39 /* Convenience macro for use with 'asm volatile' blocks */ #define __naked __attribute__((naked)) diff --git a/tools/testing/selftests/bpf/progs/verifier_mtu.c b/tools/testing/selftests/bpf/progs/verifier_mtu.c index 70c7600a26a0..4ccf1ebc42d1 100644 --- a/tools/testing/selftests/bpf/progs/verifier_mtu.c +++ b/tools/testing/selftests/bpf/progs/verifier_mtu.c @@ -6,7 +6,9 @@ SEC("tc/ingress") __description("uninit/mtu: write rejected") -__failure __msg("invalid indirect read from stack") +__success +__caps_unpriv(CAP_BPF|CAP_NET_ADMIN) +__failure_unpriv __msg_unpriv("invalid indirect read from stack") int tc_uninit_mtu(struct __sk_buff *ctx) { __u32 mtu; diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c index 3e9b009580d4..53b06647cf57 100644 --- a/tools/testing/selftests/bpf/test_loader.c +++ b/tools/testing/selftests/bpf/test_loader.c @@ -36,6 +36,7 @@ #define TEST_TAG_ARCH "comment:test_arch=" #define TEST_TAG_JITED_PFX "comment:test_jited=" #define TEST_TAG_JITED_PFX_UNPRIV "comment:test_jited_unpriv=" +#define TEST_TAG_CAPS_UNPRIV "comment:test_caps_unpriv=" /* Warning: duplicated in bpf_misc.h */ #define POINTER_VALUE 0xcafe4all @@ -74,6 +75,7 @@ struct test_subspec { struct expected_msgs jited; int retval; bool execute; + __u64 caps; }; struct test_spec { @@ -276,6 +278,37 @@ static int parse_int(const char *str, int *val, const char *name) return 0; } +static int parse_caps(const char *str, __u64 *val, const char *name) +{ + int cap_flag = 0; + char *token = NULL, *saveptr = NULL; + + char *str_cpy = strdup(str); + if (str_cpy == NULL) { + PRINT_FAIL("Memory allocation failed\n"); + return -EINVAL; + } + + token = strtok_r(str_cpy, "|", &saveptr); + while (token != NULL) { + errno = 0; + if (!strncmp("CAP_", token, sizeof("CAP_") - 1)) { + PRINT_FAIL("define %s constant in bpf_misc.h, failed to parse caps\n", token); + return -EINVAL; + } + cap_flag = strtol(token, NULL, 10); + if (!cap_flag || errno) { + PRINT_FAIL("failed to parse caps %s\n", name); + return -EINVAL; + } + *val |= (1ULL << cap_flag); + token = strtok_r(NULL, "|", &saveptr); + } + + free(str_cpy); + return 0; +} + static int parse_retval(const char *str, int *val, const char *name) { struct { @@ -541,6 +574,12 @@ static int parse_test_spec(struct test_loader *tester, jit_on_next_line = true; } else if (str_has_pfx(s, TEST_BTF_PATH)) { spec->btf_custom_path = s + sizeof(TEST_BTF_PATH) - 1; + } else if (str_has_pfx(s, TEST_TAG_CAPS_UNPRIV)) { + val = s + sizeof(TEST_TAG_CAPS_UNPRIV) - 1; + err = parse_caps(val, &spec->unpriv.caps, "test caps"); + if (err) + goto cleanup; + spec->mode_mask |= UNPRIV; } } @@ -917,6 +956,13 @@ void run_subtest(struct test_loader *tester, test__end_subtest(); return; } + if (subspec->caps) { + err = cap_enable_effective(subspec->caps, NULL); + if (err) { + PRINT_FAIL("failed to set capabilities: %i, %s\n", err, strerror(err)); + goto subtest_cleanup; + } + } } /* Implicitly reset to NULL if next test case doesn't specify */ From f513c3635078fc184af66b1af9e4f2b2d19b7d79 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Tue, 3 Dec 2024 20:47:56 -0800 Subject: [PATCH 4/5] selftests/bpf: Add test for reading from STACK_INVALID slots Ensure that when CAP_PERFMON is dropped, and the verifier sees allow_ptr_leaks as false, we are not permitted to read from a STACK_INVALID slot. Without the fix, the test will report unexpected success in loading. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241204044757.1483141-5-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/progs/verifier_spill_fill.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c index 671d9f415dbf..bab6d789ba00 100644 --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c @@ -1244,4 +1244,22 @@ __naked void old_stack_misc_vs_cur_ctx_ptr(void) : __clobber_all); } +SEC("socket") +__description("stack_noperfmon: reject read of invalid slots") +__success +__caps_unpriv(CAP_BPF) +__failure_unpriv __msg_unpriv("invalid read from stack off -8+1 size 8") +__naked void stack_noperfmon_reject_invalid_read(void) +{ + asm volatile (" \ + r2 = 1; \ + r6 = r10; \ + r6 += -8; \ + *(u8 *)(r6 + 0) = r2; \ + r2 = *(u64 *)(r6 + 0); \ + r0 = 0; \ + exit; \ +" ::: __clobber_all); +} + char _license[] SEC("license") = "GPL"; From 19b6dbc006ecc1f2c8d7fa2d5afbfb7e7eba7920 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Tue, 3 Dec 2024 20:47:57 -0800 Subject: [PATCH 5/5] selftests/bpf: Add test for narrow spill into 64-bit spilled scalar Add a test case to verify that without CAP_PERFMON, the test now succeeds instead of failing due to a verification error. Acked-by: Eduard Zingerman Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20241204044757.1483141-6-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/progs/verifier_spill_fill.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c index bab6d789ba00..1e5a511e8494 100644 --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c @@ -1262,4 +1262,21 @@ __naked void stack_noperfmon_reject_invalid_read(void) " ::: __clobber_all); } +SEC("socket") +__description("stack_noperfmon: narrow spill onto 64-bit scalar spilled slots") +__success +__caps_unpriv(CAP_BPF) +__success_unpriv +__naked void stack_noperfmon_spill_32bit_onto_64bit_slot(void) +{ + asm volatile(" \ + r0 = 0; \ + *(u64 *)(r10 - 8) = r0; \ + *(u32 *)(r10 - 8) = r0; \ + exit; \ +" : + : + : __clobber_all); +} + char _license[] SEC("license") = "GPL";