[PATCH bpf-next v2 2/3] bpf: Sanitize LDX in jited BPF progs with KASAN

Hao Sun
2022-11-25T06:36:58Z

Make the verifier sanitize LDX insns in jited BPF programs. The
dst_reg and AX are free here, different insns that backup R0&R1
are inserted based on their relationships with dst_reg and src,
all the scratch regs are backed up to extended stack space before
calling the checking functions. Finally, the checking funcs are
inserted, and regs are restored.

Signed-off-by: Hao Sun <sunhao.th@gmail.com>
---
kernel/bpf/verifier.c | 90 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 90 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5519c24c5bd4..4e253fc20bf2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -15344,6 +15344,17 @@ BPF_ASAN_STORE(16);
BPF_ASAN_STORE(32);
BPF_ASAN_STORE(64);

+#define BPF_ASAN_LOAD(n) \
+ notrace u64 bpf_asan_load##n(u##n *addr) \
+ { \
+ return *addr; \
+ }
+
+BPF_ASAN_LOAD(8);
+BPF_ASAN_LOAD(16);
+BPF_ASAN_LOAD(32);
+BPF_ASAN_LOAD(64);
+
#endif

/* Do various post-verification rewrites in a single program pass.
@@ -15588,6 +15599,85 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
insn = new_prog->insnsi + i + delta;
continue;
}
+
+ /* Sanitize LDX operation*/
+ if (BPF_CLASS(insn->code) == BPF_LDX) {
+ struct bpf_insn sanitize_fn;
+ struct bpf_insn *patch = &insn_buf[0];
+ bool dst_is_r0 = insn->dst_reg == BPF_REG_0;
+ bool dst_is_r1 = insn->dst_reg == BPF_REG_1;
+
+ if (in_patch_use_ax || insn->src_reg == BPF_REG_10)
+ continue;
+
+ switch (BPF_SIZE(insn->code)) {
+ case BPF_B:
+ sanitize_fn = BPF_EMIT_CALL(bpf_asan_load8);
+ break;
+ case BPF_H:
+ sanitize_fn = BPF_EMIT_CALL(bpf_asan_load16);
+ break;
+ case BPF_W:
+ sanitize_fn = BPF_EMIT_CALL(bpf_asan_load32);
+ break;
+ case BPF_DW:
+ sanitize_fn = BPF_EMIT_CALL(bpf_asan_load64);
+ break;
+ }
+
+ /* Backup R0 and R1, REG_AX and dst_reg are free. */
+ if (insn->src_reg == BPF_REG_1) {
+ if (!dst_is_r0)
+ *patch++ = BPF_MOV64_REG(BPF_REG_AX, BPF_REG_0);
+ } else if (insn->src_reg == BPF_REG_0) {
+ if (!dst_is_r1)
+ *patch++ = BPF_MOV64_REG(BPF_REG_AX, BPF_REG_1);
+ *patch++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_0);
+ } else if (!dst_is_r1) {
+ *patch++ = BPF_MOV64_REG(BPF_REG_AX, BPF_REG_1);
+ *patch++ = BPF_MOV64_REG(BPF_REG_1, insn->src_reg);
+ if (!dst_is_r0)
+ *patch++ = BPF_MOV64_REG(insn->dst_reg, BPF_REG_0);
+ } else {
+ *patch++ = BPF_MOV64_REG(BPF_REG_1, insn->src_reg);
+ *patch++ = BPF_MOV64_REG(BPF_REG_AX, BPF_REG_0);
+ }
+ if (insn->off != 0)
+ *patch++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, insn->off);
+ BACKUP_SCRATCH_REGS;
+ /* Invoke sanitize fn, R1~R5 are stored to stack during jit. */
+ *patch++ = sanitize_fn;
+ RESTORE_SCRATCH_REGS;
+ if (insn->off != 0)
+ *patch++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -insn->off);
+ if (insn->src_reg == BPF_REG_1) {
+ if (!dst_is_r0)
+ *patch++ = BPF_MOV64_REG(BPF_REG_0, BPF_REG_AX);
+ } else if (insn->src_reg == BPF_REG_0) {
+ *patch++ = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
+ if (!dst_is_r1)
+ *patch++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_AX);
+ } else if (!dst_is_r1) {
+ if (!dst_is_r0)
+ *patch++ = BPF_MOV64_REG(BPF_REG_0, insn->dst_reg);
+ if (insn->src_reg == insn->dst_reg)
+ *patch++ = BPF_MOV64_REG(insn->src_reg, BPF_REG_1);
+ *patch++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_AX);
+ } else {
+ *patch++ = BPF_MOV64_REG(BPF_REG_0, BPF_REG_AX);
+ }
+ *patch++ = *insn;
+ cnt = patch - insn_buf;
+
+ new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+ if (!new_prog)
+ return -ENOMEM;
+
+ delta += cnt - 1;
+ env->prog = prog = new_prog;
+ insn = new_prog->insnsi + i + delta;
+ continue;
+ }
#endif

if (insn->code != (BPF_JMP | BPF_CALL))
--
2.38.1