Merge branch 'Fixes for bad PTR_TO_BTF_ID offset'

Kumar Kartikeya Dwivedi says:

====================

This set fixes a bug related to bad var_off being permitted for kfunc call in
case of PTR_TO_BTF_ID, consolidates offset checks for all register types allowed
as helper or kfunc arguments into a common shared helper, and introduces a
couple of other checks to harden the kfunc release logic and prevent future
bugs. Some selftests are also included that fail in absence of these fixes,
serving as demonstration of the issues being fixed.

Changelog:
----------
v3 -> v4:
v3: https://lore.kernel.org/bpf/20220304000508.2904128-1-memxor@gmail.com

 * Update commit message for __diag patch to say clang instead of LLVM (Nathan)
 * Address nits for check_func_arg_reg_off (Martin)
 * Add comment for fixed_off_ok case, remove is_kfunc check (Martin)

v2 -> v3:
v2: https://lore.kernel.org/bpf/20220303045029.2645297-1-memxor@gmail.com

 * Add my SoB to __diag for clang patch (Nathan)

v1 -> v2:
v1: https://lore.kernel.org/bpf/20220301065745.1634848-1-memxor@gmail.com

 * Put reg->off check for release kfunc inside check_func_arg_reg_off,
   make the check a bit more readable
 * Squash verifier selftests errstr update into patch 3 for bisect (Alexei)
 * Include fix from Nathan for clang warning about missing prototypes
 * Add unified __diag_ingore_all that works for both GCC/LLVM (Alexei)

Older discussion:
Link: https://lore.kernel.org/bpf/20220219113744.1852259-1-memxor@gmail.com

Kumar Kartikeya Dwivedi (7):
  bpf: Add check_func_arg_reg_off function
  bpf: Fix PTR_TO_BTF_ID var_off check
  bpf: Disallow negative offset in check_ptr_off_reg
  bpf: Harden register offset checks for release helpers and kfuncs
  compiler_types.h: Add unified __diag_ignore_all for GCC/LLVM
  bpf: Replace __diag_ignore with unified __diag_ignore_all
  selftests/bpf: Add tests for kfunc register offset checks
====================
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -521,6 +521,10 @@ bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt);
 
 int check_ptr_off_reg(struct bpf_verifier_env *env,
 		      const struct bpf_reg_state *reg, int regno);
+int check_func_arg_reg_off(struct bpf_verifier_env *env,
+			   const struct bpf_reg_state *reg, int regno,
+			   enum bpf_arg_type arg_type,
+			   bool is_release_func);
 int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 			     u32 regno);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,

include/linux/compiler-clang.h

@@ -68,3 +68,28 @@
 
 #define __nocfi		__attribute__((__no_sanitize__("cfi")))
 #define __cficanonical	__attribute__((__cfi_canonical_jump_table__))
+
+/*
+ * Turn individual warnings and errors on and off locally, depending
+ * on version.
+ */
+#define __diag_clang(version, severity, s) \
+	__diag_clang_ ## version(__diag_clang_ ## severity s)
+
+/* Severity used in pragma directives */
+#define __diag_clang_ignore	ignored
+#define __diag_clang_warn	warning
+#define __diag_clang_error	error
+
+#define __diag_str1(s)		#s
+#define __diag_str(s)		__diag_str1(s)
+#define __diag(s)		_Pragma(__diag_str(clang diagnostic s))
+
+#if CONFIG_CLANG_VERSION >= 110000
+#define __diag_clang_11(s)	__diag(s)
+#else
+#define __diag_clang_11(s)
+#endif
+
+#define __diag_ignore_all(option, comment) \
+	__diag_clang(11, ignore, option)

include/linux/compiler-gcc.h

@@ -151,6 +151,9 @@
 #define __diag_GCC_8(s)
 #endif
 
+#define __diag_ignore_all(option, comment) \
+	__diag_GCC(8, ignore, option)
+
 /*
  * Prior to 9.1, -Wno-alloc-size-larger-than (and therefore the "alloc_size"
  * attribute) do not work, and must be disabled.

include/linux/compiler_types.h

@@ -371,4 +371,8 @@ struct ftrace_likely_data {
 #define __diag_error(compiler, version, option, comment) \
 	__diag_ ## compiler(version, error, option)
 
+#ifndef __diag_ignore_all
+#define __diag_ignore_all(option, comment)
+#endif
+
 #endif /* __LINUX_COMPILER_TYPES_H */

kernel/bpf/btf.c

@@ -5726,7 +5726,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 	const char *func_name, *ref_tname;
 	const struct btf_type *t, *ref_t;
 	const struct btf_param *args;
-	int ref_regno = 0;
+	int ref_regno = 0, ret;
 	bool rel = false;
 
 	t = btf_type_by_id(btf, func_id);
@@ -5753,6 +5753,10 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 		return -EINVAL;
 	}
 
+	/* Only kfunc can be release func */
+	if (is_kfunc)
+		rel = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
+						BTF_KFUNC_TYPE_RELEASE, func_id);
 	/* check that BTF function arguments match actual types that the
 	 * verifier sees.
 	 */
@@ -5776,6 +5780,11 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
 		ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
 		ref_tname = btf_name_by_offset(btf, ref_t->name_off);
+
+		ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE, rel);
+		if (ret < 0)
+			return ret;
+
 		if (btf_get_prog_ctx_type(log, btf, t,
 					  env->prog->type, i)) {
 			/* If function expects ctx type in BTF check that caller
@@ -5787,8 +5796,6 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					i, btf_type_str(t));
 				return -EINVAL;
 			}
-			if (check_ptr_off_reg(env, reg, regno))
-				return -EINVAL;
 		} else if (is_kfunc && (reg->type == PTR_TO_BTF_ID ||
 			   (reg2btf_ids[base_type(reg->type)] && !type_flag(reg->type)))) {
 			const struct btf_type *reg_ref_t;
@@ -5806,7 +5813,11 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 			if (reg->type == PTR_TO_BTF_ID) {
 				reg_btf = reg->btf;
 				reg_ref_id = reg->btf_id;
-				/* Ensure only one argument is referenced PTR_TO_BTF_ID */
+				/* Ensure only one argument is referenced
+				 * PTR_TO_BTF_ID, check_func_arg_reg_off relies
+				 * on only one referenced register being allowed
+				 * for kfuncs.
+				 */
 				if (reg->ref_obj_id) {
 					if (ref_obj_id) {
 						bpf_log(log, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
@@ -5888,18 +5899,15 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
 	/* Either both are set, or neither */
 	WARN_ON_ONCE((ref_obj_id && !ref_regno) || (!ref_obj_id && ref_regno));
-	if (is_kfunc) {
-		rel = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
-						BTF_KFUNC_TYPE_RELEASE, func_id);
-		/* We already made sure ref_obj_id is set only for one argument */
-		if (rel && !ref_obj_id) {
-			bpf_log(log, "release kernel function %s expects refcounted PTR_TO_BTF_ID\n",
-				func_name);
-			return -EINVAL;
-		}
-		/* Allow (!rel && ref_obj_id), so that passing such referenced PTR_TO_BTF_ID to
-		 * other kfuncs works
-		 */
+	/* We already made sure ref_obj_id is set only for one argument. We do
+	 * allow (!rel && ref_obj_id), so that passing such referenced
+	 * PTR_TO_BTF_ID to other kfuncs works. Note that rel is only true when
+	 * is_kfunc is true.
+	 */
+	if (rel && !ref_obj_id) {
+		bpf_log(log, "release kernel function %s expects refcounted PTR_TO_BTF_ID\n",
+			func_name);
+		return -EINVAL;
 	}
 	/* returns argument register number > 0 in case of reference release kfunc */
 	return rel ? ref_regno : 0;

kernel/bpf/verifier.c

@@ -3990,6 +3990,12 @@ static int __check_ptr_off_reg(struct bpf_verifier_env *env,
 	 * is only allowed in its original, unmodified form.
 	 */
 
+	if (reg->off < 0) {
+		verbose(env, "negative offset %s ptr R%d off=%d disallowed\n",
+			reg_type_str(env, reg->type), regno, reg->off);
+		return -EACCES;
+	}
+
 	if (!fixed_off_ok && reg->off) {
 		verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n",
 			reg_type_str(env, reg->type), regno, reg->off);
@@ -5359,6 +5365,60 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	return 0;
 }
 
+int check_func_arg_reg_off(struct bpf_verifier_env *env,
+			   const struct bpf_reg_state *reg, int regno,
+			   enum bpf_arg_type arg_type,
+			   bool is_release_func)
+{
+	bool fixed_off_ok = false, release_reg;
+	enum bpf_reg_type type = reg->type;
+
+	switch ((u32)type) {
+	case SCALAR_VALUE:
+	/* Pointer types where reg offset is explicitly allowed: */
+	case PTR_TO_PACKET:
+	case PTR_TO_PACKET_META:
+	case PTR_TO_MAP_KEY:
+	case PTR_TO_MAP_VALUE:
+	case PTR_TO_MEM:
+	case PTR_TO_MEM | MEM_RDONLY:
+	case PTR_TO_MEM | MEM_ALLOC:
+	case PTR_TO_BUF:
+	case PTR_TO_BUF | MEM_RDONLY:
+	case PTR_TO_STACK:
+		/* Some of the argument types nevertheless require a
+		 * zero register offset.
+		 */
+		if (arg_type != ARG_PTR_TO_ALLOC_MEM)
+			return 0;
+		break;
+	/* All the rest must be rejected, except PTR_TO_BTF_ID which allows
+	 * fixed offset.
+	 */
+	case PTR_TO_BTF_ID:
+		/* When referenced PTR_TO_BTF_ID is passed to release function,
+		 * it's fixed offset must be 0. We rely on the property that
+		 * only one referenced register can be passed to BPF helpers and
+		 * kfuncs. In the other cases, fixed offset can be non-zero.
+		 */
+		release_reg = is_release_func && reg->ref_obj_id;
+		if (release_reg && reg->off) {
+			verbose(env, "R%d must have zero offset when passed to release func\n",
+				regno);
+			return -EINVAL;
+		}
+		/* For release_reg == true, fixed_off_ok must be false, but we
+		 * already checked and rejected reg->off != 0 above, so set to
+		 * true to allow fixed offset for all other cases.
+		 */
+		fixed_off_ok = true;
+		break;
+	default:
+		break;
+	}
+	return __check_ptr_off_reg(env, reg, regno, fixed_off_ok);
+}
+
 static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			  struct bpf_call_arg_meta *meta,
 			  const struct bpf_func_proto *fn)
@@ -5408,36 +5468,14 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 	if (err)
 		return err;
 
-	switch ((u32)type) {
-	case SCALAR_VALUE:
-	/* Pointer types where reg offset is explicitly allowed: */
-	case PTR_TO_PACKET:
-	case PTR_TO_PACKET_META:
-	case PTR_TO_MAP_KEY:
-	case PTR_TO_MAP_VALUE:
-	case PTR_TO_MEM:
-	case PTR_TO_MEM | MEM_RDONLY:
-	case PTR_TO_MEM | MEM_ALLOC:
-	case PTR_TO_BUF:
-	case PTR_TO_BUF | MEM_RDONLY:
-	case PTR_TO_STACK:
-		/* Some of the argument types nevertheless require a
-		 * zero register offset.
-		 */
-		if (arg_type == ARG_PTR_TO_ALLOC_MEM)
-			goto force_off_check;
-		break;
-	/* All the rest must be rejected: */
-	default:
-force_off_check:
-		err = __check_ptr_off_reg(env, reg, regno,
-					  type == PTR_TO_BTF_ID);
-		if (err < 0)
-			return err;
-		break;
-	}
+	err = check_func_arg_reg_off(env, reg, regno, arg_type, is_release_function(meta->func_id));
+	if (err)
+		return err;
 
 skip_type_check:
+	/* check_func_arg_reg_off relies on only one referenced register being
+	 * allowed for BPF helpers.
+	 */
 	if (reg->ref_obj_id) {
 		if (meta->ref_obj_id) {
 			verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",

net/bpf/test_run.c

@@ -201,8 +201,8 @@ static int bpf_test_finish(const union bpf_attr *kattr,
  * future.
  */
 __diag_push();
-__diag_ignore(GCC, 8, "-Wmissing-prototypes",
-	      "Global functions as their definitions will be in vmlinux BTF");
+__diag_ignore_all("-Wmissing-prototypes",
+		  "Global functions as their definitions will be in vmlinux BTF");
 int noinline bpf_fentry_test1(int a)
 {
 	return a + 1;
@@ -270,9 +270,14 @@ struct sock * noinline bpf_kfunc_call_test3(struct sock *sk)
 	return sk;
 }
 
+struct prog_test_member {
+	u64 c;
+};
+
 struct prog_test_ref_kfunc {
 	int a;
 	int b;
+	struct prog_test_member memb;
 	struct prog_test_ref_kfunc *next;
 };
 
@@ -295,6 +300,10 @@ noinline void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p)
 {
 }
 
+noinline void bpf_kfunc_call_memb_release(struct prog_test_member *p)
+{
+}
+
 struct prog_test_pass1 {
 	int x0;
 	struct {
@@ -379,6 +388,7 @@ BTF_ID(func, bpf_kfunc_call_test2)
 BTF_ID(func, bpf_kfunc_call_test3)
 BTF_ID(func, bpf_kfunc_call_test_acquire)
 BTF_ID(func, bpf_kfunc_call_test_release)
+BTF_ID(func, bpf_kfunc_call_memb_release)
 BTF_ID(func, bpf_kfunc_call_test_pass_ctx)
 BTF_ID(func, bpf_kfunc_call_test_pass1)
 BTF_ID(func, bpf_kfunc_call_test_pass2)
@@ -396,6 +406,7 @@ BTF_SET_END(test_sk_acquire_kfunc_ids)
 
 BTF_SET_START(test_sk_release_kfunc_ids)
 BTF_ID(func, bpf_kfunc_call_test_release)
+BTF_ID(func, bpf_kfunc_call_memb_release)
 BTF_SET_END(test_sk_release_kfunc_ids)
 
 BTF_SET_START(test_sk_ret_null_kfunc_ids)

net/netfilter/nf_conntrack_bpf.c

@@ -12,6 +12,7 @@
 #include <linux/btf_ids.h>
 #include <linux/net_namespace.h>
 #include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_bpf.h>
 #include <net/netfilter/nf_conntrack_core.h>
 
 /* bpf_ct_opts - Options for CT lookup helpers
@@ -102,8 +103,8 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net,
 }
 
 __diag_push();
-__diag_ignore(GCC, 8, "-Wmissing-prototypes",
-	      "Global functions as their definitions will be in nf_conntrack BTF");
+__diag_ignore_all("-Wmissing-prototypes",
+		  "Global functions as their definitions will be in nf_conntrack BTF");
 
 /* bpf_xdp_ct_lookup - Lookup CT entry for the given tuple, and acquire a
  *		       reference to it

tools/testing/selftests/bpf/verifier/bounds_deduction.c

@@ -105,7 +105,7 @@
 		BPF_EXIT_INSN(),
 	},
 	.errstr_unpriv = "R1 has pointer with unsupported alu operation",
-	.errstr = "dereference of modified ctx ptr",
+	.errstr = "negative offset ctx ptr R1 off=-1 disallowed",
 	.result = REJECT,
 	.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
 },

tools/testing/selftests/bpf/verifier/calls.c

@@ -115,6 +115,89 @@
 		{ "bpf_kfunc_call_test_release", 5 },
 	},
 },
+{
+	"calls: invalid kfunc call: reg->off must be zero when passed to release kfunc",
+	.insns = {
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8),
+	BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
+	BPF_EXIT_INSN(),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 8),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = REJECT,
+	.errstr = "R1 must have zero offset when passed to release func",
+	.fixup_kfunc_btf_id = {
+		{ "bpf_kfunc_call_test_acquire", 3 },
+		{ "bpf_kfunc_call_memb_release", 8 },
+	},
+},
+{
+	"calls: invalid kfunc call: PTR_TO_BTF_ID with negative offset",
+	.insns = {
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8),
+	BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 16),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -4),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.fixup_kfunc_btf_id = {
+		{ "bpf_kfunc_call_test_acquire", 3 },
+		{ "bpf_kfunc_call_test_release", 9 },
+	},
+	.result_unpriv = REJECT,
+	.result = REJECT,
+	.errstr = "negative offset ptr_ ptr R1 off=-4 disallowed",
+},
+{
+	"calls: invalid kfunc call: PTR_TO_BTF_ID with variable offset",
+	.insns = {
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8),
+	BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_0, 4),
+	BPF_JMP_IMM(BPF_JLE, BPF_REG_2, 4, 3),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	BPF_JMP_IMM(BPF_JGE, BPF_REG_2, 0, 3),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_2),
+	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.fixup_kfunc_btf_id = {
+		{ "bpf_kfunc_call_test_acquire", 3 },
+		{ "bpf_kfunc_call_test_release", 9 },
+		{ "bpf_kfunc_call_test_release", 13 },
+		{ "bpf_kfunc_call_test_release", 17 },
+	},
+	.result_unpriv = REJECT,
+	.result = REJECT,
+	.errstr = "variable ptr_ access var_off=(0x0; 0x7) disallowed",
+},
 {
 	"calls: basic sanity",
 	.insns = {

tools/testing/selftests/bpf/verifier/ctx.c

@@ -58,7 +58,7 @@
 	},
 	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
 	.result = REJECT,
-	.errstr = "dereference of modified ctx ptr",
+	.errstr = "negative offset ctx ptr R1 off=-612 disallowed",
 },
 {
 	"pass modified ctx pointer to helper, 2",
@@ -71,8 +71,8 @@
 	},
 	.result_unpriv = REJECT,
 	.result = REJECT,
-	.errstr_unpriv = "dereference of modified ctx ptr",
-	.errstr = "dereference of modified ctx ptr",
+	.errstr_unpriv = "negative offset ctx ptr R1 off=-612 disallowed",
+	.errstr = "negative offset ctx ptr R1 off=-612 disallowed",
 },
 {
 	"pass modified ctx pointer to helper, 3",
@@ -141,7 +141,7 @@
 	.prog_type = BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
 	.expected_attach_type = BPF_CGROUP_UDP6_SENDMSG,
 	.result = REJECT,
-	.errstr = "dereference of modified ctx ptr",
+	.errstr = "negative offset ctx ptr R1 off=-612 disallowed",
 },
 {
 	"pass ctx or null check, 5: null (connect)",