[PATCH 2/2] x86/MCE/AMD: Skip creating kobjects with NULL names

From: Yazen Ghannam
Date: Thu Aug 09 2018 - 10:09:15 EST

From: Yazen Ghannam <yazen.ghannam@xxxxxxx>

During mce_threshold_create_device() data structures are allocated for
each CPUs MCA banks and thresholding blocks. These data structures are
used to save information related to AMD's MCA Error Thresholding
feature. The structures are used in the thresholding interrupt handler,
and they are exposed to the user through sysfs. The sysfs interface has
user-friendly names for each bank.

However, errors in mce_threshold_create_device() will cause all the data
structures to be deallocated. This will break the thresholding interrupt
handler since it depends on these structures.

One possible error is creating a kobject with a NULL name. This will
happen if a bank exists on a system that doesn't have a name, e.g. new
bank types on future systems.

Skip creating kobjects for banks without a name. This means that the
sysfs interface for this bank will not exist. But this will keep all the
data structures allocated, so the thresholding interrupt handler will
work, even for the unnamed bank. Also, the sysfs interface will still be
populated for all existing, known bank types.

Cc: <stable@xxxxxxxxxxxxxxx> # 4.13.x
Signed-off-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
arch/x86/kernel/cpu/mcheck/mce_amd.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 2dbf34250bbf..521fd8f406df 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -1130,6 +1130,7 @@ static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
struct threshold_block *b = NULL;
u32 low, high;
int err;
+ const char *name = NULL;

if ((bank >= mca_cfg.banks) || (block >= NR_BLOCKS))
return 0;
@@ -1176,9 +1177,13 @@ static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
per_cpu(threshold_banks, cpu)[bank]->blocks = b;

+ name = get_name(bank, b);
+ if (!name)
+ goto recurse;
err = kobject_init_and_add(&b->kobj, &threshold_ktype,
per_cpu(threshold_banks, cpu)[bank]->kobj,
- get_name(bank, b));
+ name);
if (err)
goto out_free;
@@ -1265,12 +1270,16 @@ static int threshold_create_bank(unsigned int cpu, unsigned int bank)
goto out;

+ if (!name)
+ goto allocate;
b->kobj = kobject_create_and_add(name, &dev->kobj);
if (!b->kobj) {
err = -EINVAL;
goto out_free;

per_cpu(threshold_banks, cpu)[bank] = b;

if (is_shared_bank(bank)) {