Re: [PATCH v2] x86/microcode: Silence a static checker warning

[Borislav Petkov]

On Thu, Aug 24, 2017 at 11:15:57PM +0300, Dan Carpenter wrote:
> The code here prints an error if "p" is an error pointer but it still
> dereferences it at the end of the function when it does:
> 
>       intel_ucode_patch = (struct microcode_intel *)__pa_nodebug(p->data);
> 
> We can just return early instead.
> 
> Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
> ---
> v2: return early instead checking for IS_ERR_OR_NULL() at the end.
> 
> We have to keep the final check whether "p" is NULL to handle the
> situation were we set "prev_found = true;" but then hit the continue
> statement instead of allocating "p".

I think we want to something more like this (not exit the loop if the
allocation fails). But I need to look at the again on a clear head:a

---
diff --git a/arch/x86/kernel/cpu/microcode/intel.c 
b/arch/x86/kernel/cpu/microcode/intel.c
index 59edbe9d4ccb..0179f0fd8a79 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -146,7 +146,7 @@ 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;
 
@@ -183,11 +183,13 @@ 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 (IS_ERR(p)) {
                                pr_err("Error allocating buffer %p\n", data);
-                       else
-                               list_replace(&iter->plist, &p->plist);
+                               continue;
+                       }
+
+                       list_replace(&iter->plist, &p->plist);
                }
        }
 
@@ -196,11 +198,12 @@ 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 (IS_ERR(p)) {
                        pr_err("Error allocating buffer for %p\n", data);
-               else
-                       list_add_tail(&p->plist, &microcode_cache);
+                       return;
+               }
+               list_add_tail(&p->plist, &microcode_cache);
        }
 
        /*

-- 
Regards/Gruss,
    Boris.

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