linux-kernel - [PATCH v3 2/9] x86/microcode/AMD: check whether the equivalence table fits in the file

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Date:   Tue, 13 Mar 2018 22:06:23 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/9] x86/microcode/AMD: check whether the equivalence table
 fits in the file

Before loading a CPU equivalence table from a microcode container file we
need to verify whether this file is actually large enough to contain the
table of a size indicated in this file.
If it is not, there is no point of continuing with loading it since
microcode patches are located after the equivalence table anyway.

Signed-off-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
---
 arch/x86/kernel/cpu/microcode/amd.c | 54 ++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index ffe0d0ce57fc..ac06e2819f26 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -80,20 +80,29 @@ static u16 find_equiv_id(struct equiv_cpu_entry *equiv_table, u32 sig)
  * Returns the amount of bytes consumed while scanning. @desc contains all the
  * data we're going to use in later stages of the application.
  */
-static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
+static size_t parse_container(u8 *ucode, size_t size, struct cont_desc *desc)
 {
 	struct equiv_cpu_entry *eq;
-	ssize_t orig_size = size;
+	size_t orig_size = size;
 	u32 *hdr = (u32 *)ucode;
+	size_t eq_size;
 	u16 eq_id;
 	u8 *buf;
 
 	/* Am I looking at an equivalence table header? */
+	if (size < CONTAINER_HDR_SZ)
+		return 0;
+
 	if (hdr[0] != UCODE_MAGIC ||
 	    hdr[1] != UCODE_EQUIV_CPU_TABLE_TYPE ||
 	    hdr[2] == 0)
 		return CONTAINER_HDR_SZ;
 
+	eq_size = hdr[2];
+	if (eq_size < sizeof(*eq) ||
+	    size - CONTAINER_HDR_SZ < eq_size)
+		return 0;
+
 	buf = ucode;
 
 	eq = (struct equiv_cpu_entry *)(buf + CONTAINER_HDR_SZ);
@@ -101,8 +110,8 @@ static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
 	/* Find the equivalence ID of our CPU in this table: */
 	eq_id = find_equiv_id(eq, desc->cpuid_1_eax);
 
-	buf  += hdr[2] + CONTAINER_HDR_SZ;
-	size -= hdr[2] + CONTAINER_HDR_SZ;
+	buf  += eq_size + CONTAINER_HDR_SZ;
+	size -= eq_size + CONTAINER_HDR_SZ;
 
 	/*
 	 * Scan through the rest of the container to find where it ends. We do
@@ -159,15 +168,13 @@ static ssize_t parse_container(u8 *ucode, ssize_t size, struct cont_desc *desc)
  */
 static void scan_containers(u8 *ucode, size_t size, struct cont_desc *desc)
 {
-	ssize_t rem = size;
-
-	while (rem >= 0) {
-		ssize_t s = parse_container(ucode, rem, desc);
+	while (size > 0) {
+		size_t s = parse_container(ucode, size, desc);
 		if (!s)
 			return;
 
 		ucode += s;
-		rem   -= s;
+		size  -= s;
 	}
 }
 
@@ -540,15 +547,30 @@ static enum ucode_state apply_microcode_amd(int cpu)
 	return UCODE_UPDATED;
 }
 
-static int install_equiv_cpu_table(const u8 *buf)
+static int install_equiv_cpu_table(const u8 *buf, size_t buf_size)
 {
 	unsigned int *ibuf = (unsigned int *)buf;
-	unsigned int type = ibuf[1];
-	unsigned int size = ibuf[2];
+	unsigned int type, size;
+
+	if (buf_size < CONTAINER_HDR_SZ) {
+		pr_err("no container header\n");
+		return -EINVAL;
+	}
+
+	type = ibuf[1];
+	if (type != UCODE_EQUIV_CPU_TABLE_TYPE) {
+		pr_err("invalid type field in container file section header\n");
+		return -EINVAL;
+	}
+
+	size = ibuf[2];
+	if (size < sizeof(struct equiv_cpu_entry)) {
+		pr_err("equivalent CPU table too short\n");
+		return -EINVAL;
+	}
 
-	if (type != UCODE_EQUIV_CPU_TABLE_TYPE || !size) {
-		pr_err("empty section/"
-		       "invalid type field in container file section header\n");
+	if (buf_size - CONTAINER_HDR_SZ < size) {
+		pr_err("equivalent CPU table truncated\n");
 		return -EINVAL;
 	}
 
@@ -655,7 +677,7 @@ static enum ucode_state __load_microcode_amd(u8 family, const u8 *data,
 	int crnt_size = 0;
 	int offset;
 
-	offset = install_equiv_cpu_table(data);
+	offset = install_equiv_cpu_table(data, size);
 	if (offset < 0) {
 		pr_err("failed to create equivalent cpu table\n");
 		return ret;