linux-kernel - [PATCH] x86/microcode/AMD: fix read of uninitialized data

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Date:   Tue, 10 Apr 2018 14:41:23 +0100
From:   Colin King <colin.king@...onical.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/microcode/AMD: fix read of uninitialized data

From: Colin Ian King <colin.king@...onical.com>

Currently function __load_ucode_amd can assign an uninitialized cp to *ret
if get_builtin_microcode returns false. This could cause function
load_ucode_amd_bsp to attempt to apply the microcode if the garbage data in
cp is non-zero.  Fix this by moving the zero'ing of cp from function
load_ucode_amd_bsp to __load_ucode_amd.

Detected by CoverityScan, CID#1398332 ("Uninitialized scalar variable")

Fixes: 69f5f983001f ("x86/microcode/AMD: Remove AP scanning optimization")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 arch/x86/kernel/cpu/microcode/amd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 0624957aa068..745135699233 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -254,7 +254,7 @@ static bool get_builtin_microcode(struct cpio_data *cp, unsigned int family)
 static void __load_ucode_amd(unsigned int cpuid_1_eax, struct cpio_data *ret)
 {
 	struct ucode_cpu_info *uci;
-	struct cpio_data cp;
+	struct cpio_data cp = { };
 	const char *path;
 	bool use_pa;
 
@@ -279,7 +279,7 @@ static void __load_ucode_amd(unsigned int cpuid_1_eax, struct cpio_data *ret)
 
 void __init load_ucode_amd_bsp(unsigned int cpuid_1_eax)
 {
-	struct cpio_data cp = { };
+	struct cpio_data cp;
 
 	__load_ucode_amd(cpuid_1_eax, &cp);
 	if (!(cp.data && cp.size))
-- 
2.15.1