Merge branch 'add-missing-size-check-for-btf-based-ctx-access'

Kumar Kartikeya Dwivedi says:

====================
Add missing size check for BTF-based ctx access

This set fixes a issue reported for tracing and struct ops programs
using btf_ctx_access for ctx checks, where loading a pointer argument
from the ctx doesn't enforce a BPF_DW access size check. The original
report is at link [0]. Also add a regression test along with the fix.

  [0]: https://lore.kernel.org/bpf/51338.1732985814@localhost
====================

Link: https://patch.msgid.link/20241212092050.3204165-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/btf.c

@@ -6543,6 +6543,12 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		return false;
 	}
 
+	if (size != sizeof(u64)) {
+		bpf_log(log, "func '%s' size %d must be 8\n",
+			tname, size);
+		return false;
+	}
+
 	/* check for PTR_TO_RDONLY_BUF_OR_NULL or PTR_TO_RDWR_BUF_OR_NULL */
 	for (i = 0; i < prog->aux->ctx_arg_info_size; i++) {
 		const struct bpf_ctx_arg_aux *ctx_arg_info = &prog->aux->ctx_arg_info[i];

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

@@ -11,7 +11,7 @@ __success __retval(0)
 __naked void btf_ctx_access_accept(void)
 {
 	asm volatile ("					\
-	r2 = *(u32*)(r1 + 8);		/* load 2nd argument value (int pointer) */\
+	r2 = *(u64 *)(r1 + 8);		/* load 2nd argument value (int pointer) */\
 	r0 = 0;						\
 	exit;						\
 "	::: __clobber_all);
@@ -23,7 +23,43 @@ __success __retval(0)
 __naked void ctx_access_u32_pointer_accept(void)
 {
 	asm volatile ("					\
-	r2 = *(u32*)(r1 + 0);		/* load 1nd argument value (u32 pointer) */\
+	r2 = *(u64 *)(r1 + 0);		/* load 1nd argument value (u32 pointer) */\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("fentry/bpf_fentry_test9")
+__description("btf_ctx_access u32 pointer reject u32")
+__failure __msg("size 4 must be 8")
+__naked void ctx_access_u32_pointer_reject_32(void)
+{
+	asm volatile ("					\
+	r2 = *(u32 *)(r1 + 0);		/* load 1st argument with narrow load */\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("fentry/bpf_fentry_test9")
+__description("btf_ctx_access u32 pointer reject u16")
+__failure __msg("size 2 must be 8")
+__naked void ctx_access_u32_pointer_reject_16(void)
+{
+	asm volatile ("					\
+	r2 = *(u16 *)(r1 + 0);		/* load 1st argument with narrow load */\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("fentry/bpf_fentry_test9")
+__description("btf_ctx_access u32 pointer reject u8")
+__failure __msg("size 1 must be 8")
+__naked void ctx_access_u32_pointer_reject_8(void)
+{
+	asm volatile ("					\
+	r2 = *(u8 *)(r1 + 0);		/* load 1st argument with narrow load */\
 	r0 = 0;						\
 	exit;						\
 "	::: __clobber_all);

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

@@ -11,7 +11,7 @@ __success __retval(0)
 __naked void d_path_accept(void)
 {
 	asm volatile ("					\
-	r1 = *(u32*)(r1 + 0);				\
+	r1 = *(u64 *)(r1 + 0);				\
 	r2 = r10;					\
 	r2 += -8;					\
 	r6 = 0;						\
@@ -31,7 +31,7 @@ __failure __msg("helper call is not allowed in probe")
 __naked void d_path_reject(void)
 {
 	asm volatile ("					\
-	r1 = *(u32*)(r1 + 0);				\
+	r1 = *(u64 *)(r1 + 0);				\
 	r2 = r10;					\
 	r2 += -8;					\
 	r6 = 0;						\