selftests/bpf: Test stack arguments across may_goto

Each test passes arguments 6-8 on the stack. Thus it uses all the registers
in which the JITs of x86-64, arm64 and riscv64 pass stack arguments.

  may_goto                                     then
  -------------------------------------------  ---------------------------
  70000 iterations in the callee               the callee reads the args
  the time is up in the callee                 the callee reads the args
  70000 iterations in the caller, after the    the caller calls the callee
  writes of the args

70000 iterations have one look at the clock. Without the fix on x86-64 the
second test fails, and the first test fails with the hpet clocksource. The
third test passes there. The result depends on the registers that the C
code uses.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261027190314.1440199-20-alexei.starovoitov@gmail.com

1 files changed, 119 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
index b9f799f6e405..15a12497e074 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -433,6 +433,125 @@ __naked void stack_arg_sequential_calls(void)
 	);
 }
 
+/*
+ * A JIT passes the first stack arguments in registers. may_goto is not a call: they must be
+ * the same after it, also when it looks at the clock. That is once in 65535 iterations.
+ */
+__naked __noinline __used
+static long loops_then_reads_8args(long a, long b, long c, long d, long e, long f, long g, long h)
+{
+	asm volatile (
+		"r1 = 0;"
+	"1:"
+		"may_goto 2f;"
+		"r1 += 1;"
+		"if r1 < 70000 goto 1b;"
+	"2:"
+		"r0 = *(u64 *)(r11 + 8);"
+		"r1 = *(u64 *)(r11 + 16);"
+		"r0 += r1;"
+		"r1 = *(u64 *)(r11 + 24);"
+		"r0 += r1;"
+		"exit;"
+	);
+}
+
+SEC("tc")
+__description("stack_arg: may_goto looks at the clock, then the callee reads its args")
+__success __retval(876)
+__naked void stack_arg_may_goto_in_callee(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r11 - 24) = 800;"
+		"*(u64 *)(r11 - 16) = 70;"
+		"*(u64 *)(r11 - 8) = 6;"
+		"call loops_then_reads_8args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+__naked __noinline __used
+static long spins_then_reads_8args(long a, long b, long c, long d, long e, long f, long g, long h)
+{
+	asm volatile (
+	"1:"
+		"may_goto 2f;"
+		"goto 1b;"
+	"2:"
+		"r0 = *(u64 *)(r11 + 8);"
+		"r1 = *(u64 *)(r11 + 16);"
+		"r0 += r1;"
+		"r1 = *(u64 *)(r11 + 24);"
+		"r0 += r1;"
+		"exit;"
+	);
+}
+
+SEC("tc")
+__description("stack_arg: the time of may_goto is up, then the callee reads its args")
+__success __retval(876)
+__naked void stack_arg_may_goto_timeout_in_callee(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r11 - 24) = 800;"
+		"*(u64 *)(r11 - 16) = 70;"
+		"*(u64 *)(r11 - 8) = 6;"
+		"call spins_then_reads_8args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+__naked __noinline __used
+static long reads_8args(long a, long b, long c, long d, long e, long f, long g, long h)
+{
+	asm volatile (
+		"r0 = *(u64 *)(r11 + 8);"
+		"r1 = *(u64 *)(r11 + 16);"
+		"r0 += r1;"
+		"r1 = *(u64 *)(r11 + 24);"
+		"r0 += r1;"
+		"exit;"
+	);
+}
+
+SEC("tc")
+__description("stack_arg: may_goto looks at the clock between the stores of the args and the call")
+__success __retval(876)
+__naked void stack_arg_may_goto_in_caller(void)
+{
+	asm volatile (
+		"*(u64 *)(r11 - 24) = 800;"
+		"*(u64 *)(r11 - 16) = 70;"
+		"*(u64 *)(r11 - 8) = 6;"
+		"r6 = 0;"
+	"1:"
+		"may_goto 2f;"
+		"r6 += 1;"
+		"if r6 < 70000 goto 1b;"
+	"2:"
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"call reads_8args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
 #else
 
 SEC("socket")