bpf: Fix helper writes to read-only maps

Lonial found an issue that despite user- and BPF-side frozen BPF map
(like in case of .rodata), it was still possible to write into it from
a BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT}
as arguments.

In check_func_arg() when the argument is as mentioned, the meta->raw_mode
is never set. Later, check_helper_mem_access(), under the case of
PTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the
subsequent call to check_map_access_type() and given the BPF map is
read-only it succeeds.

The helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT
when results are written into them as opposed to read out of them. The
latter indicates that it's okay to pass a pointer to uninitialized memory
as the memory is written to anyway.

However, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM
just with additional alignment requirement. So it is better to just get
rid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the
fixed size memory types. For this, add MEM_ALIGNED to additionally ensure
alignment given these helpers write directly into the args via *<ptr> = val.
The .arg*_size has been initialized reflecting the actual sizeof(*<ptr>).

MEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated
argument types, since in !MEM_FIXED_SIZE cases the verifier does not know
the buffer size a priori and therefore cannot blindly write *<ptr> = val.

Fixes: 57c3bb725a3d ("bpf: Introduce ARG_PTR_TO_{INT,LONG} arg types")
Reported-by: Lonial Con <kongln9170@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Link: https://lore.kernel.org/r/20240913191754.13290-3-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 11 insertions, 39 deletions

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5404bb964d83..5e97fdc6b20f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -537,7 +537,8 @@ const struct bpf_func_proto bpf_strtol_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
 	.arg2_type	= ARG_CONST_SIZE,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(s64),
 };
 
 BPF_CALL_4(bpf_strtoul, const char *, buf, size_t, buf_len, u64, flags,
@@ -563,7 +564,8 @@ const struct bpf_func_proto bpf_strtoul_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
 	.arg2_type	= ARG_CONST_SIZE,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(u64),
 };
 
 BPF_CALL_3(bpf_strncmp, const char *, s1, u32, s1_sz, const char *, s2)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6988e432fc3d..a7cd3719e26a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5954,7 +5954,8 @@ static const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {
 	.arg1_type	= ARG_PTR_TO_MEM,
 	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
 	.arg3_type	= ARG_ANYTHING,
-	.arg4_type	= ARG_PTR_TO_LONG,
+	.arg4_type	= ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_ALIGNED,
+	.arg4_size	= sizeof(u64),
 };
 
 static const struct bpf_func_proto *
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 068f763dcefb..7d62fd576089 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8301,16 +8301,6 @@ static bool arg_type_is_dynptr(enum bpf_arg_type type)
 	return base_type(type) == ARG_PTR_TO_DYNPTR;
 }
 
-static int int_ptr_type_to_size(enum bpf_arg_type type)
-{
-	if (type == ARG_PTR_TO_INT)
-		return sizeof(u32);
-	else if (type == ARG_PTR_TO_LONG)
-		return sizeof(u64);
-
-	return -EINVAL;
-}
-
 static int resolve_map_arg_type(struct bpf_verifier_env *env,
 				 const struct bpf_call_arg_meta *meta,
 				 enum bpf_arg_type *arg_type)
@@ -8383,16 +8373,6 @@ static const struct bpf_reg_types mem_types = {
 	},
 };
 
-static const struct bpf_reg_types int_ptr_types = {
-	.types = {
-		PTR_TO_STACK,
-		PTR_TO_PACKET,
-		PTR_TO_PACKET_META,
-		PTR_TO_MAP_KEY,
-		PTR_TO_MAP_VALUE,
-	},
-};
-
 static const struct bpf_reg_types spin_lock_types = {
 	.types = {
 		PTR_TO_MAP_VALUE,
@@ -8453,8 +8433,6 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 	[ARG_PTR_TO_SPIN_LOCK]		= &spin_lock_types,
 	[ARG_PTR_TO_MEM]		= &mem_types,
 	[ARG_PTR_TO_RINGBUF_MEM]	= &ringbuf_mem_types,
-	[ARG_PTR_TO_INT]		= &int_ptr_types,
-	[ARG_PTR_TO_LONG]		= &int_ptr_types,
 	[ARG_PTR_TO_PERCPU_BTF_ID]	= &percpu_btf_ptr_types,
 	[ARG_PTR_TO_FUNC]		= &func_ptr_types,
 	[ARG_PTR_TO_STACK]		= &stack_ptr_types,
@@ -9017,9 +8995,11 @@ skip_type_check:
 		 */
 		meta->raw_mode = arg_type & MEM_UNINIT;
 		if (arg_type & MEM_FIXED_SIZE) {
-			err = check_helper_mem_access(env, regno,
-						      fn->arg_size[arg], false,
-						      meta);
+			err = check_helper_mem_access(env, regno, fn->arg_size[arg], false, meta);
+			if (err)
+				return err;
+			if (arg_type & MEM_ALIGNED)
+				err = check_ptr_alignment(env, reg, 0, fn->arg_size[arg], true);
 		}
 		break;
 	case ARG_CONST_SIZE:
@@ -9044,17 +9024,6 @@ skip_type_check:
 		if (err)
 			return err;
 		break;
-	case ARG_PTR_TO_INT:
-	case ARG_PTR_TO_LONG:
-	{
-		int size = int_ptr_type_to_size(arg_type);
-
-		err = check_helper_mem_access(env, regno, size, false, meta);
-		if (err)
-			return err;
-		err = check_ptr_alignment(env, reg, 0, size, true);
-		break;
-	}
 	case ARG_PTR_TO_CONST_STR:
 	{
 		err = check_reg_const_str(env, reg, regno);