linux-kernel - [PATCH bpf-next v3 2/3] bpf: Sanitize LDX in jited BPF progs with KASAN

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Date:   Fri, 25 Nov 2022 20:29:11 +0800
From:   Hao Sun <sunhao.th@...il.com>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, Hao Sun <sunhao.th@...il.com>
Subject: [PATCH bpf-next v3 2/3] bpf: Sanitize LDX in jited BPF progs with KASAN

Make the verifier sanitize LDX insns in jited BPF programs. Saved
all the scratch regs to the extended stack first, skip backing up
of R0 if it is the dst_reg, then save checking addr to R1. Finally
the checking funcs are inserted, and regs are restored then.

Signed-off-by: Hao Sun <sunhao.th@...il.com>
---
 kernel/bpf/verifier.c | 60 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7a31fceee370..b3b6855a9756 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -15345,6 +15345,18 @@ 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); \
+	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.
@@ -15567,6 +15579,54 @@ 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];
+
+			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_SCRATCH_REGS;
+			/* Skip R0, if it is dst but not src */
+			if (insn->dst_reg != BPF_REG_0 || insn->src_reg == BPF_REG_0)
+				*patch++ = BPF_MOV64_REG(BPF_REG_AX, BPF_REG_0);
+			if (insn->src_reg != BPF_REG_1)
+				*patch++ = BPF_MOV64_REG(BPF_REG_1, insn->src_reg);
+			if (insn->off != 0)
+				*patch++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, insn->off);
+			*patch++ = sanitize_fn;
+			RESTORE_SCRATCH_REGS;
+			if (insn->dst_reg != BPF_REG_0 || insn->src_reg == BPF_REG_0)
+				*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