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Subject[tip: ras/urgent] x86/mce/amd: Publish the bank pointer only after setup has succeeded
The following commit has been merged into the ras/urgent branch of tip:

Commit-ID: 6e5cf31fbe651bed7ba1df768f2e123531132417
Gitweb: https://git.kernel.org/tip/6e5cf31fbe651bed7ba1df768f2e123531132417
Author: Borislav Petkov <bp@suse.de>
AuthorDate: Tue, 04 Feb 2020 13:28:41 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 13 Feb 2020 18:58:39 +01:00

x86/mce/amd: Publish the bank pointer only after setup has succeeded

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
---
arch/x86/kernel/cpu/mce/amd.c | 33 ++++++++++++++++-----------------
1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index b3a50d9..e7313e5 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1198,8 +1198,9 @@ 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;
@@ -1243,16 +1244,12 @@ 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:
@@ -1260,7 +1257,7 @@ recurse:
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;

@@ -1345,8 +1342,6 @@ 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);

@@ -1357,9 +1352,13 @@ 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);
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