From 3ffbb2e3c0cba7e91f8eb9d1ac03b4b7deda8793 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@suse.de>
Date: Tue, 4 Feb 2020 13:28:41 +0100
Subject: [PATCH] x86/mce/amd: Publish the bank pointer only after setup has
 succeeded

commit 6e5cf31fbe651bed7ba1df768f2e123531132417 upstream.

threshold_create_bank() creates a bank descriptor per MCA error
thresholding counter which can be controlled over sysfs. It publishes
the pointer to that bank in a per-CPU variable and then goes on to
create additional thresholding blocks if the bank has such.

However, that creation of additional blocks in
allocate_threshold_blocks() can fail, leading to a use-after-free
through the per-CPU pointer.

Therefore, publish that pointer only after all blocks have been setup
successfully.

Fixes: 019f34fccfd5 ("x86, MCE, AMD: Move shared bank to node descriptor")
Reported-by: Saar Amar <Saar.Amar@microsoft.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200128140846.phctkvx5btiexvbx@kili.mountain
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 303b8c58845e..740d95ea05d2 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1194,8 +1194,9 @@ static const char *get_name(unsigned int bank, struct threshold_block *b)
 	return buf_mcatype;
 }
 
-static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
-				     unsigned int block, u32 address)
+static int allocate_threshold_blocks(unsigned int cpu, struct threshold_bank *tb,
+				     unsigned int bank, unsigned int block,
+				     u32 address)
 {
 	struct threshold_block *b = NULL;
 	u32 low, high;
@@ -1239,16 +1240,12 @@ static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
 
 	INIT_LIST_HEAD(&b->miscj);
 
-	if (per_cpu(threshold_banks, cpu)[bank]->blocks) {
-		list_add(&b->miscj,
-			 &per_cpu(threshold_banks, cpu)[bank]->blocks->miscj);
-	} else {
-		per_cpu(threshold_banks, cpu)[bank]->blocks = b;
-	}
+	if (tb->blocks)
+		list_add(&b->miscj, &tb->blocks->miscj);
+	else
+		tb->blocks = b;
 
-	err = kobject_init_and_add(&b->kobj, &threshold_ktype,
-				   per_cpu(threshold_banks, cpu)[bank]->kobj,
-				   get_name(bank, b));
+	err = kobject_init_and_add(&b->kobj, &threshold_ktype, tb->kobj, get_name(bank, b));
 	if (err)
 		goto out_free;
 recurse:
@@ -1256,7 +1253,7 @@ static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
 	if (!address)
 		return 0;
 
-	err = allocate_threshold_blocks(cpu, bank, block, address);
+	err = allocate_threshold_blocks(cpu, tb, bank, block, address);
 	if (err)
 		goto out_free;
 
@@ -1341,8 +1338,6 @@ static int threshold_create_bank(unsigned int cpu, unsigned int bank)
 		goto out_free;
 	}
 
-	per_cpu(threshold_banks, cpu)[bank] = b;
-
 	if (is_shared_bank(bank)) {
 		refcount_set(&b->cpus, 1);
 
@@ -1353,9 +1348,13 @@ static int threshold_create_bank(unsigned int cpu, unsigned int bank)
 		}
 	}
 
-	err = allocate_threshold_blocks(cpu, bank, 0, msr_ops.misc(bank));
-	if (!err)
-		goto out;
+	err = allocate_threshold_blocks(cpu, b, bank, 0, msr_ops.misc(bank));
+	if (err)
+		goto out_free;
+
+	per_cpu(threshold_banks, cpu)[bank] = b;
+
+	return 0;
 
  out_free:
 	kfree(b);
-- 
2.7.4