[bpf-next,v3,2/6] bpf: Improve check_raw_mode_ok test for MEM_UNINIT-tagged types

Commit Message

Daniel Borkmann Sept. 5, 2024, 1:48 p.m. UTC

When checking malformed helper function signatures, also take other argument
types into account aside from just ARG_PTR_TO_UNINIT_MEM.

This concerns (formerly) ARG_PTR_TO_{INT,LONG} given uninitialized memory can
be passed there, too.

The func proto sanity check goes back to commit 435faee1aae9 ("bpf, verifier:
add ARG_PTR_TO_RAW_STACK type"), and its purpose was to detect wrong func protos
which had more than just one MEM_UNINIT-tagged type as arguments.

The reason more than one is currently not supported is as we mark stack slots with
STACK_MISC in check_helper_call() in case of raw mode based on meta.access_size to
allow uninitialized stack memory to be passed to helpers when they just write into
the buffer.

Probing for base type as well as MEM_UNINIT tagging ensures that other types do not
get missed (as it used to be the case for ARG_PTR_TO_{INT,LONG}).

Fixes: 57c3bb725a3d ("bpf: Introduce ARG_PTR_TO_{INT,LONG} arg types")
Reported-by: Shung-Hsi Yu <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
---
 v1 -> v2:
 - new patch (Shung-Hsi)
 v2 -> v3:
 - base_type(type) was needed also

 kernel/bpf/verifier.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index efd9c453399e..26240637c863 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8296,6 +8296,12 @@  static bool arg_type_is_mem_size(enum bpf_arg_type type)
 	       type == ARG_CONST_SIZE_OR_ZERO;
 }
 
+static bool arg_type_is_raw_mem(enum bpf_arg_type type)
+{
+	return base_type(type) == ARG_PTR_TO_MEM &&
+	       type & MEM_UNINIT;
+}
+
 static bool arg_type_is_release(enum bpf_arg_type type)
 {
 	return type & OBJ_RELEASE;
@@ -9348,15 +9354,15 @@  static bool check_raw_mode_ok(const struct bpf_func_proto *fn)
 {
 	int count = 0;
 
-	if (fn->arg1_type == ARG_PTR_TO_UNINIT_MEM)
+	if (arg_type_is_raw_mem(fn->arg1_type))
 		count++;
-	if (fn->arg2_type == ARG_PTR_TO_UNINIT_MEM)
+	if (arg_type_is_raw_mem(fn->arg2_type))
 		count++;
-	if (fn->arg3_type == ARG_PTR_TO_UNINIT_MEM)
+	if (arg_type_is_raw_mem(fn->arg3_type))
 		count++;
-	if (fn->arg4_type == ARG_PTR_TO_UNINIT_MEM)
+	if (arg_type_is_raw_mem(fn->arg4_type))
 		count++;
-	if (fn->arg5_type == ARG_PTR_TO_UNINIT_MEM)
+	if (arg_type_is_raw_mem(fn->arg5_type))
 		count++;
 
 	/* We only support one arg being in raw mode at the moment,