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Subject[PATCH] x86/microcode/intel: Improve microcode patches saving flow
From: Borislav Petkov <bp@suse.de>

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>
---
arch/x86/kernel/cpu/microcode/intel.c | 27 ++++++++++++++-------------
1 file 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)
--
2.13.0

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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