x86/microcode/intel: Improve microcode patches saving flow

Avoid potentially dereferencing a NULL pointer when saving a microcode
patch for early loading on the application processors.

While at it, drop the IS_ERR() checking in favor of simpler, NULL-ptr
checks which are sufficient and rename __alloc_microcode_buf() to
memdup_patch() to more precisely denote what it does.

No functionality change.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Link: http://lkml.kernel.org/r/20170825100456.n236w3jebteokfd6@pd.tnic

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 59edbe9d4ccbb1500b82136a5061abb057bd333e..8f7a9bbad514efbec73ed1beb167c7d8432521b2 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -146,18 +146,18 @@ static bool microcode_matches(struct microcode_header_intel *mc_header,
        return false;
 }
 
-static struct ucode_patch *__alloc_microcode_buf(void *data, unsigned int size)
+static struct ucode_patch *memdup_patch(void *data, unsigned int size)
 {
        struct ucode_patch *p;
 
        p = kzalloc(sizeof(struct ucode_patch), GFP_KERNEL);
        if (!p)
-               return ERR_PTR(-ENOMEM);
+               return NULL;
 
        p->data = kmemdup(data, size, GFP_KERNEL);
        if (!p->data) {
                kfree(p);
-               return ERR_PTR(-ENOMEM);
+               return NULL;
        }
 
        return p;
@@ -183,8 +183,8 @@ static void save_microcode_patch(void *data, unsigned int size)
                        if (mc_hdr->rev <= mc_saved_hdr->rev)
                                continue;
 
-                       p = __alloc_microcode_buf(data, size);
-                       if (IS_ERR(p))
+                       p = memdup_patch(data, size);
+                       if (!p)
                                pr_err("Error allocating buffer %p\n", data);
                        else
                                list_replace(&iter->plist, &p->plist);
@@ -196,24 +196,25 @@ static void save_microcode_patch(void *data, unsigned int size)
         * newly found.
         */
        if (!prev_found) {
-               p = __alloc_microcode_buf(data, size);
-               if (IS_ERR(p))
+               p = memdup_patch(data, size);
+               if (!p)
                        pr_err("Error allocating buffer for %p\n", data);
                else
                        list_add_tail(&p->plist, &microcode_cache);
        }
 
+       if (!p)
+               return;
+
        /*
         * Save for early loading. On 32-bit, that needs to be a physical
         * address as the APs are running from physical addresses, before
         * paging has been enabled.
         */
-       if (p) {
-               if (IS_ENABLED(CONFIG_X86_32))
-                       intel_ucode_patch = (struct microcode_intel *)__pa_nodebug(p->data);
-               else
-                       intel_ucode_patch = p->data;
-       }
+       if (IS_ENABLED(CONFIG_X86_32))
+               intel_ucode_patch = (struct microcode_intel *)__pa_nodebug(p->data);
+       else
+               intel_ucode_patch = p->data;
 }
 
 static int microcode_sanity_check(void *mc, int print_err)