Commit 2a33c5a2 authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Alexei Starovoitov
Browse files

selftests/bpf: check if BPF_ST with variable offset preserves STACK_ZERO 



A test case to verify that variable offset BPF_ST instruction
preserves STACK_ZERO marks when writes zeros, e.g. in the following
situation:

  *(u64*)(r10 - 8) = 0   ; STACK_ZERO marks for fp[-8]
  r0 = random(-7, -1)    ; some random number in range of [-7, -1]
  r0 += r10              ; r0 is now variable offset pointer to stack
  *(u8*)(r0) = 0         ; BPF_ST writing zero, STACK_ZERO mark for
                         ; fp[-8] should be preserved.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230214232030.1502829-5-eddyz87@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 31ff2135

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

+30 −0
Original line number Diff line number Diff line
@@ -35,3 +35,33 @@ 
	.expected_attach_type = BPF_SK_LOOKUP,

	.runs = -1,

},

{

	"BPF_ST_MEM stack imm zero, variable offset",

	.insns = {

	/* set fp[-16], fp[-24] to zeros */

	BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),

	BPF_ST_MEM(BPF_DW, BPF_REG_10, -24, 0),

	/* r0 = random value in range [-32, -15] */

	BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32),

	BPF_JMP_IMM(BPF_JLE, BPF_REG_0, 16, 2),

	BPF_MOV64_IMM(BPF_REG_0, 0),

	BPF_EXIT_INSN(),

	BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 32),

	/* fp[r0] = 0, make a variable offset write of zero,

	 *             this should preserve zero marks on stack.

	 */

	BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_10),

	BPF_ST_MEM(BPF_B, BPF_REG_0, 0, 0),

	/* r0 = fp[-20], if variable offset write was tracked correctly

	 *               r0 would be a known zero.

	 */

	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_10, -20),

	/* Would fail return code verification if r0 range is not tracked correctly. */

	BPF_EXIT_INSN(),

	},

	.result = ACCEPT,

	/* Use prog type that requires return value in range [0, 1] */

	.prog_type = BPF_PROG_TYPE_SK_LOOKUP,

	.expected_attach_type = BPF_SK_LOOKUP,

	.runs = -1,

},