netdev - [PATCH bpf-next v2 05/15] selftests/bpf: Add a test case for 32-bit spill tracking

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Message-ID: <20240108205209.838365-6-maxtram95@gmail.com>
Date: Mon,  8 Jan 2024 22:51:59 +0200
From: Maxim Mikityanskiy <maxtram95@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Shung-Hsi Yu <shung-hsi.yu@...e.com>
Cc: John Fastabend <john.fastabend@...il.com>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	netdev@...r.kernel.org,
	Maxim Mikityanskiy <maxim@...valent.com>
Subject: [PATCH bpf-next v2 05/15] selftests/bpf: Add a test case for 32-bit spill tracking

From: Maxim Mikityanskiy <maxim@...valent.com>

When a range check is performed on a register that was 32-bit spilled to
the stack, the IDs of the two instances of the register are the same, so
the range should also be the same.

Signed-off-by: Maxim Mikityanskiy <maxim@...valent.com>
Acked-by: Eduard Zingerman <eddyz87@...il.com>
---
 .../selftests/bpf/progs/verifier_spill_fill.c | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
index 848f2930f599..f303ac19cf41 100644
--- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
+++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c
@@ -735,4 +735,35 @@ __naked void stack_load_preserves_const_precision_subreg(void)
 	: __clobber_common);
 }
 
+SEC("xdp")
+__description("32-bit spilled reg range should be tracked")
+__success __retval(0)
+__naked void spill_32bit_range_track(void)
+{
+	asm volatile("					\
+	call %[bpf_ktime_get_ns];			\
+	/* Make r0 bounded. */				\
+	r0 &= 65535;					\
+	/* Assign an ID to r0. */			\
+	r1 = r0;					\
+	/* 32-bit spill r0 to stack. */			\
+	*(u32*)(r10 - 8) = r0;				\
+	/* Boundary check on r0. */			\
+	if r0 < 1 goto l0_%=;				\
+	/* 32-bit fill r1 from stack. */		\
+	r1 = *(u32*)(r10 - 8);				\
+	/* r1 == r0 => r1 >= 1 always. */		\
+	if r1 >= 1 goto l0_%=;				\
+	/* Dead branch: the verifier should prune it.   \
+	 * Do an invalid memory access if the verifier	\
+	 * follows it.					\
+	 */						\
+	r0 = *(u64*)(r9 + 0);				\
+l0_%=:	r0 = 0;						\
+	exit;						\
+"	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0