linux-kernel - [PATCH 2/3] x86/apic: Make apic

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Date:	Fri,  2 Oct 2015 21:12:24 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Daniel J Blueman <daniel@...ascale.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <len.brown@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] x86/apic: Make apic_version[] smaller

apic_version[] array is changed from int to u8 -
APIC version values as of year 2015 are no larger than 0x1f
on all known CPUs.

A bit of code added to ensure that the statement
    apic_version[apicid] = version;
in generic_processor_info() is safe wrt bad values in both
'apicid' and 'version' variables.

This reduces apic_version[] from 128 kbytes to 32.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Ingo Molnar <mingo@...nel.org>
CC: Daniel J Blueman <daniel@...ascale.com>
CC: Jiang Liu <jiang.liu@...ux.intel.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Len Brown <len.brown@...el.com>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/include/asm/mpspec.h |  2 +-
 arch/x86/kernel/apic/apic.c   | 19 ++++++++++++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/mpspec.h b/arch/x86/include/asm/mpspec.h
index e84e542..83140ab 100644
--- a/arch/x86/include/asm/mpspec.h
+++ b/arch/x86/include/asm/mpspec.h
@@ -6,7 +6,7 @@
 #include <asm/x86_init.h>
 #include <asm/apicdef.h>
 
-extern int apic_version[];
+extern u8 apic_version[];
 extern int pic_mode;
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b08b447..d0f135c 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1798,7 +1798,7 @@ void __init register_lapic_address(unsigned long address)
 	}
 }
 
-int apic_version[MAX_LOCAL_APICID];
+u8 apic_version[MAX_LOCAL_APICID];
 
 /*
  * Local APIC interrupts
@@ -2054,6 +2054,23 @@ int generic_processor_info(int apicid, int version)
 		return -EINVAL;
 	}
 
+	if ((unsigned)apicid >= ARRAY_SIZE(apic_version)) {
+		int thiscpu = max + disabled_cpus;
+		pr_warning("APIC: APIC id 0x%x is too large."
+			   " Processor %d ignored.\n",
+			   apicid, thiscpu);
+		disabled_cpus++;
+		return -EINVAL;
+	}
+	if ((unsigned)version > 255) {
+		int thiscpu = max + disabled_cpus;
+		pr_warning("APIC: APIC version 0x%x is too large."
+			   " Processor %d ignored.\n",
+			   version, thiscpu);
+		disabled_cpus++;
+		return -EINVAL;
+	}
+
 	num_processors++;
 	if (apicid == boot_cpu_physical_apicid) {
 		/*
-- 
1.8.1.4

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