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 --- .../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, +},