Subject: [PATCH] bpf, x32: Fix bug for BPF_JMP | {BPF_JSGT, BPF_JSLE, BPF_JSLT, BPF_JSGE}

From: Wang YanQing <[email-masked]>
Date: Fri, 26 Apr 2019 18:56:09 +0800

The current method to compare 64-bit numbers for conditional jump is:

1) Compare the high 32-bit first.

2) If the high 32-bit isn't the same, then goto step 4.

3) Compare the low 32-bit.

4) Check the desired condition.

This method is right for unsigned comparison, but it is buggy for signed
comparison, because it does signed comparison for low 32-bit too.

There is only one sign bit in 64-bit number, that is the MSB in the 64-bit
number, it is wrong to treat low 32-bit as signed number and do the signed
comparison for it.

This patch fixes the bug.

Signed-off-by: Wang YanQing <[email-masked]>
---
 arch/x86/net/bpf_jit_comp32.c | 217 ++++++++++++++++++++++++++++++++----------
 1 file changed, 166 insertions(+), 51 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 0d9cdff..c431e15 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -117,6 +117,8 @@ static bool is_simm32(s64 value)
 #define IA32_JLE 0x7E
 #define IA32_JG  0x7F
 
+#define COND_JMP_OPCODE_INVALID	(0xFF)
+
 /*
  * Map eBPF registers to IA32 32bit registers or stack scratch space.
  *
@@ -1613,6 +1615,75 @@ static inline void emit_push_r64(const u8 src[], u8 **pprog)
 	*pprog = prog;
 }
 
+static u8 get_cond_jmp_opcode(const u8 op, bool is_cmp_lo)
+{
+	u8 jmp_cond;
+
+	/* Convert BPF opcode to x86 */
+	switch (op) {
+	case BPF_JEQ:
+		jmp_cond = IA32_JE;
+		break;
+	case BPF_JSET:
+	case BPF_JNE:
+		jmp_cond = IA32_JNE;
+		break;
+	case BPF_JGT:
+		/* GT is unsigned '>', JA in x86 */
+		jmp_cond = IA32_JA;
+		break;
+	case BPF_JLT:
+		/* LT is unsigned '<', JB in x86 */
+		jmp_cond = IA32_JB;
+		break;
+	case BPF_JGE:
+		/* GE is unsigned '>=', JAE in x86 */
+		jmp_cond = IA32_JAE;
+		break;
+	case BPF_JLE:
+		/* LE is unsigned '<=', JBE in x86 */
+		jmp_cond = IA32_JBE;
+		break;
+	case BPF_JSGT:
+		if (!is_cmp_lo)
+			/* Signed '>', GT in x86 */
+			jmp_cond = IA32_JG;
+		else
+			/* GT is unsigned '>', JA in x86 */
+			jmp_cond = IA32_JA;
+		break;
+	case BPF_JSLT:
+		if (!is_cmp_lo)
+			/* Signed '<', LT in x86 */
+			jmp_cond = IA32_JL;
+		else
+			/* LT is unsigned '<', JB in x86 */
+			jmp_cond = IA32_JB;
+		break;
+	case BPF_JSGE:
+		if (!is_cmp_lo)
+			/* Signed '>=', GE in x86 */
+			jmp_cond = IA32_JGE;
+		else
+			/* GE is unsigned '>=', JAE in x86 */
+			jmp_cond = IA32_JAE;
+		break;
+	case BPF_JSLE:
+		if (!is_cmp_lo)
+			/* Signed '<=', LE in x86 */
+			jmp_cond = IA32_JLE;
+		else
+			/* LE is unsigned '<=', JBE in x86 */
+			jmp_cond = IA32_JBE;
+		break;
+	default: /* to silence GCC warning */
+		jmp_cond = COND_JMP_OPCODE_INVALID;
+		break;
+	}
+
+	return jmp_cond;
+}
+
 static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		  int oldproglen, struct jit_context *ctx)
 {
@@ -2069,10 +2140,6 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_JMP | BPF_JLT | BPF_X:
 		case BPF_JMP | BPF_JGE | BPF_X:
 		case BPF_JMP | BPF_JLE | BPF_X:
-		case BPF_JMP | BPF_JSGT | BPF_X:
-		case BPF_JMP | BPF_JSLE | BPF_X:
-		case BPF_JMP | BPF_JSLT | BPF_X:
-		case BPF_JMP | BPF_JSGE | BPF_X:
 		case BPF_JMP32 | BPF_JEQ | BPF_X:
 		case BPF_JMP32 | BPF_JNE | BPF_X:
 		case BPF_JMP32 | BPF_JGT | BPF_X:
@@ -2118,6 +2185,40 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			EMIT2(0x39, add_2reg(0xC0, dreg_lo, sreg_lo));
 			goto emit_cond_jmp;
 		}
+		case BPF_JMP | BPF_JSGT | BPF_X:
+		case BPF_JMP | BPF_JSLE | BPF_X:
+		case BPF_JMP | BPF_JSLT | BPF_X:
+		case BPF_JMP | BPF_JSGE | BPF_X: {
+			u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
+			u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+			u8 sreg_lo = sstk ? IA32_ECX : src_lo;
+			u8 sreg_hi = sstk ? IA32_EBX : src_hi;
+
+			if (dstk) {
+				EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EAX),
+				      STACK_VAR(dst_lo));
+				EMIT3(0x8B,
+				      add_2reg(0x40, IA32_EBP,
+					       IA32_EDX),
+				      STACK_VAR(dst_hi));
+			}
+
+			if (sstk) {
+				EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_ECX),
+				      STACK_VAR(src_lo));
+				EMIT3(0x8B,
+				      add_2reg(0x40, IA32_EBP,
+					       IA32_EBX),
+				      STACK_VAR(src_hi));
+			}
+
+			/* cmp dreg_hi,sreg_hi */
+			EMIT2(0x39, add_2reg(0xC0, dreg_hi, sreg_hi));
+			EMIT2(IA32_JNE, 10);
+			/* cmp dreg_lo,sreg_lo */
+			EMIT2(0x39, add_2reg(0xC0, dreg_lo, sreg_lo));
+			goto emit_cond_jmp_signed;
+		}
 		case BPF_JMP | BPF_JSET | BPF_X:
 		case BPF_JMP32 | BPF_JSET | BPF_X: {
 			bool is_jmp64 = BPF_CLASS(insn->code) == BPF_JMP;
@@ -2194,10 +2295,6 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_JMP | BPF_JLT | BPF_K:
 		case BPF_JMP | BPF_JGE | BPF_K:
 		case BPF_JMP | BPF_JLE | BPF_K:
-		case BPF_JMP | BPF_JSGT | BPF_K:
-		case BPF_JMP | BPF_JSLE | BPF_K:
-		case BPF_JMP | BPF_JSLT | BPF_K:
-		case BPF_JMP | BPF_JSGE | BPF_K:
 		case BPF_JMP32 | BPF_JEQ | BPF_K:
 		case BPF_JMP32 | BPF_JNE | BPF_K:
 		case BPF_JMP32 | BPF_JGT | BPF_K:
@@ -2238,50 +2335,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			/* cmp dreg_lo,sreg_lo */
 			EMIT2(0x39, add_2reg(0xC0, dreg_lo, sreg_lo));
 
-emit_cond_jmp:		/* Convert BPF opcode to x86 */
-			switch (BPF_OP(code)) {
-			case BPF_JEQ:
-				jmp_cond = IA32_JE;
-				break;
-			case BPF_JSET:
-			case BPF_JNE:
-				jmp_cond = IA32_JNE;
-				break;
-			case BPF_JGT:
-				/* GT is unsigned '>', JA in x86 */
-				jmp_cond = IA32_JA;
-				break;
-			case BPF_JLT:
-				/* LT is unsigned '<', JB in x86 */
-				jmp_cond = IA32_JB;
-				break;
-			case BPF_JGE:
-				/* GE is unsigned '>=', JAE in x86 */
-				jmp_cond = IA32_JAE;
-				break;
-			case BPF_JLE:
-				/* LE is unsigned '<=', JBE in x86 */
-				jmp_cond = IA32_JBE;
-				break;
-			case BPF_JSGT:
-				/* Signed '>', GT in x86 */
-				jmp_cond = IA32_JG;
-				break;
-			case BPF_JSLT:
-				/* Signed '<', LT in x86 */
-				jmp_cond = IA32_JL;
-				break;
-			case BPF_JSGE:
-				/* Signed '>=', GE in x86 */
-				jmp_cond = IA32_JGE;
-				break;
-			case BPF_JSLE:
-				/* Signed '<=', LE in x86 */
-				jmp_cond = IA32_JLE;
-				break;
-			default: /* to silence GCC warning */
+emit_cond_jmp:		jmp_cond = get_cond_jmp_opcode(BPF_OP(code), false);
+			if (jmp_cond == COND_JMP_OPCODE_INVALID)
 				return -EFAULT;
-			}
 			jmp_offset = addrs[i + insn->off] - addrs[i];
 			if (is_imm8(jmp_offset)) {
 				EMIT2(jmp_cond, jmp_offset);
@@ -2291,7 +2347,66 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 				pr_err("cond_jmp gen bug %llx\n", jmp_offset);
 				return -EFAULT;
 			}
+			break;
+		}
+		case BPF_JMP | BPF_JSGT | BPF_K:
+		case BPF_JMP | BPF_JSLE | BPF_K:
+		case BPF_JMP | BPF_JSLT | BPF_K:
+		case BPF_JMP | BPF_JSGE | BPF_K: {
+			u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
+			u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+			u8 sreg_lo = IA32_ECX;
+			u8 sreg_hi = IA32_EBX;
+			u32 hi;
+
+			if (dstk) {
+				EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EAX),
+				      STACK_VAR(dst_lo));
+				EMIT3(0x8B,
+				      add_2reg(0x40, IA32_EBP,
+					       IA32_EDX),
+				      STACK_VAR(dst_hi));
+			}
+
+			/* mov ecx,imm32 */
+			EMIT2_off32(0xC7, add_1reg(0xC0, IA32_ECX), imm32);
+			hi = imm32 & (1 << 31) ? (u32)~0 : 0;
+			/* mov ebx,imm32 */
+			EMIT2_off32(0xC7, add_1reg(0xC0, IA32_EBX), hi);
+			/* cmp dreg_hi,sreg_hi */
+			EMIT2(0x39, add_2reg(0xC0, dreg_hi, sreg_hi));
+			EMIT2(IA32_JNE, 10);
+			/* cmp dreg_lo,sreg_lo */
+			EMIT2(0x39, add_2reg(0xC0, dreg_lo, sreg_lo));
+
+			/*
+			 * For simplicity of branch offset computation,
+			 * let's use fix jump coding here.
+			 */
+emit_cond_jmp_signed:	/* Check the condition for low 32-bit comparison */
+			jmp_cond = get_cond_jmp_opcode(BPF_OP(code), true);
+			if (jmp_cond == COND_JMP_OPCODE_INVALID)
+				return -EFAULT;
+			jmp_offset = addrs[i + insn->off] - addrs[i] + 8;
+			if (is_simm32(jmp_offset)) {
+				EMIT2_off32(0x0F, jmp_cond + 0x10, jmp_offset);
+			} else {
+				pr_err("cond_jmp gen bug %llx\n", jmp_offset);
+				return -EFAULT;
+			}
+			EMIT2(0xEB, 6);
 
+			/* Check the condition for high 32-bit comparison */
+			jmp_cond = get_cond_jmp_opcode(BPF_OP(code), false);
+			if (jmp_cond == COND_JMP_OPCODE_INVALID)
+				return -EFAULT;
+			jmp_offset = addrs[i + insn->off] - addrs[i];
+			if (is_simm32(jmp_offset)) {
+				EMIT2_off32(0x0F, jmp_cond + 0x10, jmp_offset);
+			} else {
+				pr_err("cond_jmp gen bug %llx\n", jmp_offset);
+				return -EFAULT;
+			}
 			break;
 		}
 		case BPF_JMP | BPF_JA:
-- 
1.8.5.6.2.g3d8a54e.dirty