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

1 files changed, 14 insertions, 13 deletions

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 59edbe9d4ccb..8f7a9bbad514 100644
--- 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)