linux-kernel - [PATCH bpf 2/2] bpf, selftests: Add test for BPF_STX BPF

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Message-Id: <20200418232655.23870-2-luke.r.nels@gmail.com>
Date:   Sat, 18 Apr 2020 16:26:54 -0700
From:   Luke Nelson <lukenels@...washington.edu>
To:     bpf@...r.kernel.org
Cc:     Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: [PATCH bpf 2/2] bpf, selftests: Add test for BPF_STX BPF_B storing R10

This patch adds a test to test_verifier that writes the lower 8 bits of
R10 (aka FP) using BPF_B to an array map and reads the result back. The
expected behavior is that the result should be the same as first copying
R10 to R9, and then storing / loading the lower 8 bits of R9.

This test catches a bug that was present in the x86-64 JIT that caused
an incorrect encoding for BPF_STX BPF_B when the source operand is R10.

Signed-off-by: Xi Wang <xi.wang@...il.com>
Signed-off-by: Luke Nelson <luke.r.nels@...il.com>
---
 .../selftests/bpf/verifier/stack_ptr.c        | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/tools/testing/selftests/bpf/verifier/stack_ptr.c b/tools/testing/selftests/bpf/verifier/stack_ptr.c
index 7276620ef242..8bfeb77c60bd 100644
--- a/tools/testing/selftests/bpf/verifier/stack_ptr.c
+++ b/tools/testing/selftests/bpf/verifier/stack_ptr.c
@@ -315,3 +315,43 @@
 	},
 	.result = ACCEPT,
 },
+{
+	"store PTR_TO_STACK in R10 to array map using BPF_B",
+	.insns = {
+	/* Load pointer to map. */
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+	BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
+	BPF_LD_MAP_FD(BPF_REG_1, 0),
+	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	/* Copy R10 to R9. */
+	BPF_MOV64_REG(BPF_REG_9, BPF_REG_10),
+	/* Pollute other registers with unaligned values. */
+	BPF_MOV64_IMM(BPF_REG_2, -1),
+	BPF_MOV64_IMM(BPF_REG_3, -1),
+	BPF_MOV64_IMM(BPF_REG_4, -1),
+	BPF_MOV64_IMM(BPF_REG_5, -1),
+	BPF_MOV64_IMM(BPF_REG_6, -1),
+	BPF_MOV64_IMM(BPF_REG_7, -1),
+	BPF_MOV64_IMM(BPF_REG_8, -1),
+	/* Store both R9 and R10 with BPF_B and read back. */
+	BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_10, 0),
+	BPF_LDX_MEM(BPF_B, BPF_REG_2, BPF_REG_1, 0),
+	BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_9, 0),
+	BPF_LDX_MEM(BPF_B, BPF_REG_3, BPF_REG_1, 0),
+	/* Should read back as same value. */
+	BPF_JMP_REG(BPF_JEQ, BPF_REG_2, BPF_REG_3, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_IMM(BPF_REG_0, 42),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_array_48b = { 3 },
+	.result = ACCEPT,
+	.retval = 42,
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+},
-- 
2.17.1