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@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200418232655.23870-2-luke.r.nels@gmail.com

diff --git a/tools/testing/selftests/bpf/verifier/stack_ptr.c b/tools/testing/selftests/bpf/verifier/stack_ptr.c
index 7276620..8bfeb77 100644 (file)
--- 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,
+},