selftests/bpf: Add dynptr pruning tests

Add verifier tests that verify the new pruning behavior for STACK_DYNPTR
slots, and ensure that state equivalence takes into account changes to
the old and current verifier state correctly. Also ensure that the
stacksafe changes are actually enabling pruning in case states are
equivalent from pruning PoV.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230121002241.2113993-10-memxor@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -35,6 +35,13 @@ struct {
 	__type(value, __u32);
 } array_map3 SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} array_map4 SEC(".maps");
+
 struct sample {
 	int pid;
 	long value;
@@ -653,3 +660,137 @@ int dynptr_from_mem_invalid_api(void *ctx)
 
 	return 0;
 }
+
+SEC("?tc")
+__failure __msg("cannot overwrite referenced dynptr") __log_level(2)
+int dynptr_pruning_overwrite(struct __sk_buff *ctx)
+{
+	asm volatile (
+		"r9 = 0xeB9F;				\
+		 r6 = %[ringbuf] ll;			\
+		 r1 = r6;				\
+		 r2 = 8;				\
+		 r3 = 0;				\
+		 r4 = r10;				\
+		 r4 += -16;				\
+		 call %[bpf_ringbuf_reserve_dynptr];	\
+		 if r0 == 0 goto pjmp1;			\
+		 goto pjmp2;				\
+	pjmp1:						\
+		 *(u64 *)(r10 - 16) = r9;		\
+	pjmp2:						\
+		 r1 = r10;				\
+		 r1 += -16;				\
+		 r2 = 0;				\
+		 call %[bpf_ringbuf_discard_dynptr];	"
+		:
+		: __imm(bpf_ringbuf_reserve_dynptr),
+		  __imm(bpf_ringbuf_discard_dynptr),
+		  __imm_addr(ringbuf)
+		: __clobber_all
+	);
+	return 0;
+}
+
+SEC("?tc")
+__success __msg("12: safe") __log_level(2)
+int dynptr_pruning_stacksafe(struct __sk_buff *ctx)
+{
+	asm volatile (
+		"r9 = 0xeB9F;				\
+		 r6 = %[ringbuf] ll;			\
+		 r1 = r6;				\
+		 r2 = 8;				\
+		 r3 = 0;				\
+		 r4 = r10;				\
+		 r4 += -16;				\
+		 call %[bpf_ringbuf_reserve_dynptr];	\
+		 if r0 == 0 goto stjmp1;		\
+		 goto stjmp2;				\
+	stjmp1:						\
+		 r9 = r9;				\
+	stjmp2:						\
+		 r1 = r10;				\
+		 r1 += -16;				\
+		 r2 = 0;				\
+		 call %[bpf_ringbuf_discard_dynptr];	"
+		:
+		: __imm(bpf_ringbuf_reserve_dynptr),
+		  __imm(bpf_ringbuf_discard_dynptr),
+		  __imm_addr(ringbuf)
+		: __clobber_all
+	);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("cannot overwrite referenced dynptr") __log_level(2)
+int dynptr_pruning_type_confusion(struct __sk_buff *ctx)
+{
+	asm volatile (
+		"r6 = %[array_map4] ll;			\
+		 r7 = %[ringbuf] ll;			\
+		 r1 = r6;				\
+		 r2 = r10;				\
+		 r2 += -8;				\
+		 r9 = 0;				\
+		 *(u64 *)(r2 + 0) = r9;			\
+		 r3 = r10;				\
+		 r3 += -24;				\
+		 r9 = 0xeB9FeB9F;			\
+		 *(u64 *)(r10 - 16) = r9;		\
+		 *(u64 *)(r10 - 24) = r9;		\
+		 r9 = 0;				\
+		 r4 = 0;				\
+		 r8 = r2;				\
+		 call %[bpf_map_update_elem];		\
+		 r1 = r6;				\
+		 r2 = r8;				\
+		 call %[bpf_map_lookup_elem];		\
+		 if r0 != 0 goto tjmp1;			\
+		 exit;					\
+	tjmp1:						\
+		 r8 = r0;				\
+		 r1 = r7;				\
+		 r2 = 8;				\
+		 r3 = 0;				\
+		 r4 = r10;				\
+		 r4 += -16;				\
+		 r0 = *(u64 *)(r0 + 0);			\
+		 call %[bpf_ringbuf_reserve_dynptr];	\
+		 if r0 == 0 goto tjmp2;			\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 r8 = r8;				\
+		 goto tjmp3;				\
+	tjmp2:						\
+		 *(u64 *)(r10 - 8) = r9;		\
+		 *(u64 *)(r10 - 16) = r9;		\
+		 r1 = r8;				\
+		 r1 += 8;				\
+		 r2 = 0;				\
+		 r3 = 0;				\
+		 r4 = r10;				\
+		 r4 += -16;				\
+		 call %[bpf_dynptr_from_mem];		\
+	tjmp3:						\
+		 r1 = r10;				\
+		 r1 += -16;				\
+		 r2 = 0;				\
+		 call %[bpf_ringbuf_discard_dynptr];	"
+		:
+		: __imm(bpf_map_update_elem),
+		  __imm(bpf_map_lookup_elem),
+		  __imm(bpf_ringbuf_reserve_dynptr),
+		  __imm(bpf_dynptr_from_mem),
+		  __imm(bpf_ringbuf_discard_dynptr),
+		  __imm_addr(array_map4),
+		  __imm_addr(ringbuf)
+		: __clobber_all
+	);
+	return 0;
+}