linux-kernel - [PATCH v2 05/21] x86/insn-eval: Handle return values from the decoder

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Date:   Wed, 24 Feb 2021 12:02:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 05/21] x86/insn-eval: Handle return values from the decoder

From: Borislav Petkov <bp@...e.de>

Now that the different instruction-inspecting functions return a value,
test that and return early from callers if error has been encountered.

While at it, do not call insn_get_modrm() when calling
insn_get_displacement() because latter will make sure to call
insn_get_modrm() if ModRM hasn't been parsed yet.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/lib/insn-eval.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index d0ebf9e93e35..1a6c191a38f8 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -928,10 +928,11 @@ static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs,
 static int get_eff_addr_reg(struct insn *insn, struct pt_regs *regs,
 			    int *regoff, long *eff_addr)
 {
-	insn_get_modrm(insn);
+	int ret;
 
-	if (!insn->modrm.nbytes)
-		return -EINVAL;
+	ret = insn_get_modrm(insn);
+	if (ret)
+		return ret;
 
 	if (X86_MODRM_MOD(insn->modrm.value) != 3)
 		return -EINVAL;
@@ -977,14 +978,14 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs,
 			      int *regoff, long *eff_addr)
 {
 	long tmp;
+	int ret;
 
 	if (insn->addr_bytes != 8 && insn->addr_bytes != 4)
 		return -EINVAL;
 
-	insn_get_modrm(insn);
-
-	if (!insn->modrm.nbytes)
-		return -EINVAL;
+	ret = insn_get_modrm(insn);
+	if (ret)
+		return ret;
 
 	if (X86_MODRM_MOD(insn->modrm.value) > 2)
 		return -EINVAL;
@@ -1106,18 +1107,21 @@ static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs,
  * @base_offset will have a register, as an offset from the base of pt_regs,
  * that can be used to resolve the associated segment.
  *
- * -EINVAL on error.
+ * Negative value on error.
  */
 static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs,
 			    int *base_offset, long *eff_addr)
 {
 	long base, indx;
 	int indx_offset;
+	int ret;
 
 	if (insn->addr_bytes != 8 && insn->addr_bytes != 4)
 		return -EINVAL;
 
-	insn_get_modrm(insn);
+	ret = insn_get_modrm(insn);
+	if (ret)
+		return ret;
 
 	if (!insn->modrm.nbytes)
 		return -EINVAL;
@@ -1125,7 +1129,9 @@ static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs,
 	if (X86_MODRM_MOD(insn->modrm.value) > 2)
 		return -EINVAL;
 
-	insn_get_sib(insn);
+	ret = insn_get_sib(insn);
+	if (ret)
+		return ret;
 
 	if (!insn->sib.nbytes)
 		return -EINVAL;
@@ -1194,8 +1200,8 @@ static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs)
 	short eff_addr;
 	long tmp;
 
-	insn_get_modrm(insn);
-	insn_get_displacement(insn);
+	if (insn_get_displacement(insn))
+		goto out;
 
 	if (insn->addr_bytes != 2)
 		goto out;
@@ -1491,7 +1497,9 @@ bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs,
 	insn->addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
 	insn->opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
 
-	insn_get_length(insn);
+	if (insn_get_length(insn))
+		return false;
+
 	if (buf_size < insn->length)
 		return false;
 
-- 
2.29.2