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Subject[PATCH 5/7] x86/mce: Convert threshold_bank.cpus from atomic_t to refcount_t
Date
From: Elena Reshetova <elena.reshetova@intel.com>

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>
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>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/1492695536-5947-1-git-send-email-elena.reshetova@intel.com
Signed-off-by: Borislav Petkov <bp@suse.de>
---
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 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;
--
2.11.0
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