selftests/bpf: Add a selftest for checking subreg equality

Add a selftest to ensure subreg equality if source register
upper 32bit is 0. Without previous patch, the test will
fail verification.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230417222139.360607-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -31,6 +31,7 @@
 #include "verifier_meta_access.skel.h"
 #include "verifier_raw_stack.skel.h"
 #include "verifier_raw_tp_writable.skel.h"
+#include "verifier_reg_equal.skel.h"
 #include "verifier_ringbuf.skel.h"
 #include "verifier_spill_fill.skel.h"
 #include "verifier_stack_ptr.skel.h"
@@ -95,6 +96,7 @@ void test_verifier_masking(void)              { RUN(verifier_masking); }
 void test_verifier_meta_access(void)          { RUN(verifier_meta_access); }
 void test_verifier_raw_stack(void)            { RUN(verifier_raw_stack); }
 void test_verifier_raw_tp_writable(void)      { RUN(verifier_raw_tp_writable); }
+void test_verifier_reg_equal(void)            { RUN(verifier_reg_equal); }
 void test_verifier_ringbuf(void)              { RUN(verifier_ringbuf); }
 void test_verifier_spill_fill(void)           { RUN(verifier_spill_fill); }
 void test_verifier_stack_ptr(void)            { RUN(verifier_stack_ptr); }

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

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+SEC("socket")
+__description("check w reg equal if r reg upper32 bits 0")
+__success
+__naked void subreg_equality_1(void)
+{
+	asm volatile ("					\
+	call %[bpf_ktime_get_ns];			\
+	*(u64 *)(r10 - 8) = r0;				\
+	r2 = *(u32 *)(r10 - 8);				\
+	/* At this point upper 4-bytes of r2 are 0,	\
+	 * thus insn w3 = w2 should propagate reg id,	\
+	 * and w2 < 9 comparison would also propagate	\
+	 * the range for r3.				\
+	 */						\
+	w3 = w2;					\
+	if w2 < 9 goto l0_%=;				\
+	exit;						\
+l0_%=:	if r3 < 9 goto l1_%=;				\
+	/* r1 read is illegal at this point */		\
+	r0 -= r1;					\
+l1_%=:	exit;						\
+"	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("check w reg not equal if r reg upper32 bits not 0")
+__failure __msg("R1 !read_ok")
+__naked void subreg_equality_2(void)
+{
+	asm volatile ("					\
+	call %[bpf_ktime_get_ns];			\
+	r2 = r0;					\
+	/* Upper 4-bytes of r2 may not be 0, thus insn	\
+	 * w3 = w2 should not propagate reg id,	and	\
+	 * w2 < 9 comparison should not propagate	\
+	 * the range for r3 either.			\
+	 */						\
+	w3 = w2;					\
+	if w2 < 9 goto l0_%=;				\
+	exit;						\
+l0_%=:	if r3 < 9 goto l1_%=;				\
+	/* r1 read is illegal at this point */		\
+	r0 -= r1;					\
+l1_%=:	exit;						\
+"	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+char _license[] SEC("license") = "GPL";