[PATCH bpf-next v4 11/18] selftests/bpf: Check liveness merge of masks with different widths

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

The liveness masks of a function instance are as wide as the deepest
half-slot the instance was seen to access. When the same instance is
analyzed again through another call site, the new pass may have settled
on a different width, and merge_instances() has to widen the original
before combining the two. Add a test where the first pass of a callee
reads through a pointer 248 bytes into the main frame and the second
one through a pointer of unknown offset, which reads the whole frame,
and check that the merged result keeps the whole-frame read. The
precise read stays within the first mask word on 64-bit, so the
whole-frame pass is wider under every stack budget and the merge has
to widen the masks; a deeper read would need two words already, which
is all a 512-byte whole-frame read needs on 64-bit, and the widening
would go untested there.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/progs/verifier_live_stack.c | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_live_stack.c b/tools/testing/selftests/bpf/progs/verifier_live_stack.c
index f8758eb62dac..c3b08089fef1 100644
--- a/tools/testing/selftests/bpf/progs/verifier_live_stack.c
+++ b/tools/testing/selftests/bpf/progs/verifier_live_stack.c
@@ -2861,3 +2861,54 @@ __naked void narrow_store_defines_nothing(void)
 	"exit;"
 	::: __clobber_all);
 }
+
+/*
+ * The same callee instance is analyzed twice: the call sites are visited in
+ * postorder, so the second one goes first with a precise pointer 248 bytes
+ * into the main frame, and the first one then passes a pointer of unknown
+ * offset, which reads the whole frame. The precise pass stays within the
+ * first word of the masks on 64-bit, so the whole-frame pass is wider under
+ * every stack budget and merging the second into the first has to widen the
+ * masks while keeping the whole-frame read.
+ */
+SEC("socket")
+__log_level(2)
+__msg("stack use/def subprog#{{[0-9]+}} merge_read_all_callee (d2,cs{{[0-9]+}}):")
+__msg("(79) r0 = *(u64 *)(r1 +0){{.*}}; use: fp0-8..-512")
+__naked void merge_keeps_whole_frame_read(void)
+{
+	asm volatile (
+	"r1 = 0;"
+	"*(u64 *)(r10 - 8) = r1;"
+	"*(u64 *)(r10 - 16) = r1;"
+	"*(u64 *)(r10 - 248) = r1;"
+	"call %[bpf_get_prandom_u32];"
+	"r0 &= 8;"
+	"r1 = r10;"
+	"r1 += -16;"
+	"r1 += r0;"
+	"call merge_read_all_mid;"
+	"r1 = r10;"
+	"r1 += -248;"
+	"call merge_read_all_mid;"
+	"r0 = 0;"
+	"exit;"
+	:: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+static __used __naked void merge_read_all_mid(void)
+{
+	asm volatile (
+	"call merge_read_all_callee;"
+	"exit;"
+	::: __clobber_all);
+}
+
+static __used __naked void merge_read_all_callee(void)
+{
+	asm volatile (
+	"r0 = *(u64 *)(r1 + 0);"
+	"exit;"
+	::: __clobber_all);
+}
-- 
2.53.0