x86/MCE/AMD: Cache SMCA MISC block addresses

... into a global, two-dimensional array and service subsequent reads from
that cache to avoid rdmsr_on_cpu() calls during CPU hotplug (IPIs with IRQs
disabled).

In addition, this fixes a KASAN slab-out-of-bounds read due to wrong usage
of the bank->blocks pointer.

Fixes: 27bd59502702 ("x86/mce/AMD: Get address from already initialized block")
Reported-by: Johannes Hirte <[e-mail]>
Tested-by: Johannes Hirte <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: Yazen Ghannam <[e-mail]>
Link: http://lkml.kernel.org/r/20180414004230.GA2033@probook

arch/x86/kernel/cpu/mcheck/mce_amd.c

···
 	[SMCA_SMU]	= { "smu",		"System Management Unit" },
 };
 
+static u32 smca_bank_addrs[MAX_NR_BANKS][NR_BLOCKS] __ro_after_init =
+{
+	[0 ... MAX_NR_BANKS - 1] = { [0 ... NR_BLOCKS - 1] = -1 }
+};
+
 const char *smca_get_name(enum smca_bank_types t)
 {
 	if (t >= N_SMCA_BANK_TYPES)
···
 	if (!block)
 		return MSR_AMD64_SMCA_MCx_MISC(bank);
 
+	/* Check our cache first: */
+	if (smca_bank_addrs[bank][block] != -1)
+		return smca_bank_addrs[bank][block];
+
 	/*
 	 * For SMCA enabled processors, BLKPTR field of the first MISC register
 	 * (MCx_MISC0) indicates presence of additional MISC regs set (MISC1-4).
 	 */
 	if (rdmsr_safe_on_cpu(cpu, MSR_AMD64_SMCA_MCx_CONFIG(bank), &low, &high))
-		return addr;
+		goto out;
 
 	if (!(low & MCI_CONFIG_MCAX))
-		return addr;
+		goto out;
 
 	if (!rdmsr_safe_on_cpu(cpu, MSR_AMD64_SMCA_MCx_MISC(bank), &low, &high) &&
 	    (low & MASK_BLKPTR_LO))
-		return MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);
+		addr = MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);
 
+out:
+	smca_bank_addrs[bank][block] = addr;
 	return addr;
 }
 
···
 
 	if ((bank >= mca_cfg.banks) || (block >= NR_BLOCKS))
 		return addr;
-
-	/* Get address from already initialized block. */
-	if (per_cpu(threshold_banks, cpu)) {
-		struct threshold_bank *bankp = per_cpu(threshold_banks, cpu)[bank];
-
-		if (bankp && bankp->blocks) {
-			struct threshold_block *blockp = &bankp->blocks[block];
-
-			if (blockp)
-				return blockp->address;
-		}
-	}
 
 	if (mce_flags.smca)
 		return smca_get_block_address(cpu, bank, block);