[PATCH 1/2] x86/MCE/AMD: Check for NULL banks in THR interrupt handler

[Yazen Ghannam]

From: Yazen Ghannam <yazen.ghan...@amd.com>

If threshold_init_device() fails then per_cpu(threshold_banks) will be
deallocated. The thresholding interrupt handler will still be active, so
it's possible to get a NULL pointer dereference if a THR interrupt
happens and any of the structures are NULL.

Exit the handler if per_cpu(threshold_banks) is NULL and skip NULL
banks. MCA error information will still be in the registers. The
information will be logged during polling or in another MCA exception or
interrupt handler.

Fixes: 17ef4af0ec0f ("x86/mce/AMD: Use saved threshold block info in interrupt 
handler")
Cc: <sta...@vger.kernel.org> # 4.13.x
Signed-off-by: Yazen Ghannam <yazen.ghan...@amd.com>
---
 arch/x86/kernel/cpu/mcheck/mce_amd.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c 
b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index dd33c357548f..2dbf34250bbf 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -934,13 +934,21 @@ static void log_and_reset_block(struct threshold_block 
*block)
 static void amd_threshold_interrupt(void)
 {
        struct threshold_block *first_block = NULL, *block = NULL, *tmp = NULL;
+       struct threshold_bank *th_bank = NULL;
        unsigned int bank, cpu = smp_processor_id();
 
+       if (!per_cpu(threshold_banks, cpu))
+               return;
+
        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                if (!(per_cpu(bank_map, cpu) & (1 << bank)))
                        continue;
 
-               first_block = per_cpu(threshold_banks, cpu)[bank]->blocks;
+               th_bank = per_cpu(threshold_banks, cpu)[bank];
+               if (!th_bank)
+                       continue;
+
+               first_block = th_bank->blocks;
                if (!first_block)
                        continue;
 
-- 
2.17.1