Merge branch 'fixes-for-stack-with-allow_ptr_leaks'

Kumar Kartikeya Dwivedi says:

====================
Fixes for stack with allow_ptr_leaks

Two fixes for usability/correctness gaps when interacting with the stack
without CAP_PERFMON (i.e. with allow_ptr_leaks = false). See the commits
for details. I've verified that the tests fail when run without the fixes.

Changelog:
----------
v3 -> v4
v3: https://lore.kernel.org/bpf/20241202083814.1888784-1-memxor@gmail.com

 * Address Andrii's comments
   * Fix bug paperered over by missing CAP_NET_ADMIN in verifier_mtu
     test
   * Add warning when undefined CAP_ constant is specified, and fail
     test
   * Reorder annotations to be more clear
   * Verify that fixes fail without patches again
 * Add Acked-by from Andrii

v2 -> v3
v2: https://lore.kernel.org/bpf/20241127212026.3580542-1-memxor@gmail.com

 * Address comments from Eduard
   * Fix comment for mark_stack_slot_misc
   * We can simply always return early when stype == STACK_INVALID
   * Drop allow_ptr_leaks conditionals
   * Add Eduard's __caps_unpriv patch into the series
   * Convert test_verifier_mtu to use it
   * Move existing tests to __caps_unpriv annotation and verifier_spill_fill.c
   * Add Acked-by from Eduard

v1 -> v2
v1: https://lore.kernel.org/bpf/20241127185135.2753982-1-memxor@gmail.com

 * Fix CI errors in selftest by removing dependence on BPF_ST
====================

Link: https://patch.msgid.link/20241204044757.1483141-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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;
 }
@@ -4700,6 +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;

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)
 {

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))

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;

tools/testing/selftests/bpf/progs/verifier_spill_fill.c

@@ -1244,4 +1244,39 @@ __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);
+}
+
+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";

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 */