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Subject[PATCH] x86: convert threshold_bank.cpus from atomic_t to refcount_t
Date
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>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Reviewed-by: David Windsor <dwindsor@gmail.com>
---
arch/x86/include/asm/amd_nb.h | 3 ++-
arch/x86/kernel/cpu/mcheck/mce_amd.c | 6 +++---
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 00c88a0..da181ad 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 524cc57..cfe0838 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;
--
2.7.4
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