x86/mce: Convert threshold_bank.cpus from atomic_t to refcount_t

The refcount_t type and corresponding API should be used instead
of atomic_t when the variable is used as a reference counter. This
allows to avoid accidental refcounter overflows that might lead to
use-after-free situations.

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Yazen Ghannam <Yazen.Ghannam@amd.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1492695536-5947-1-git-send-email-elena.reshetova@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 5 insertions, 4 deletions

diff --git a/arch/x86/include/asm/amd_nb.h b/arch/x86/include/asm/amd_nb.h
index 00c88a01301d..da181ad1d5f8 100644
--- a/arch/x86/include/asm/amd_nb.h
+++ b/arch/x86/include/asm/amd_nb.h
@@ -3,6 +3,7 @@
 
 #include <linux/ioport.h>
 #include <linux/pci.h>
+#include <linux/refcount.h>
 
 struct amd_nb_bus_dev_range {
         u8 bus;
@@ -55,7 +56,7 @@ struct threshold_bank {
         struct threshold_block  *blocks;
 
         /* initialized to the number of CPUs on the node sharing this bank */
-        atomic_t                cpus;
+        refcount_t              cpus;
 };
 
 struct amd_northbridge {
diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 6e4a047e4b68..41439ab41102 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -1202,7 +1202,7 @@ static int threshold_create_bank(unsigned int cpu, unsigned int bank)
                                 goto out;
 
                         per_cpu(threshold_banks, cpu)[bank] = b;
-                        atomic_inc(&b->cpus);
+                        refcount_inc(&b->cpus);
 
                         err = __threshold_add_blocks(b);
 
@@ -1225,7 +1225,7 @@ static int threshold_create_bank(unsigned int cpu, unsigned int bank)
         per_cpu(threshold_banks, cpu)[bank] = b;
 
         if (is_shared_bank(bank)) {
-                atomic_set(&b->cpus, 1);
+                refcount_set(&b->cpus, 1);
 
                 /* nb is already initialized, see above */
                 if (nb) {
@@ -1289,7 +1289,7 @@ static void threshold_remove_bank(unsigned int cpu, int bank)
                 goto free_out;
 
         if (is_shared_bank(bank)) {
-                if (!atomic_dec_and_test(&b->cpus)) {
+                if (!refcount_dec_and_test(&b->cpus)) {
                         __threshold_remove_blocks(b);
                         per_cpu(threshold_banks, cpu)[bank] = NULL;
                         return;