linux-kernel - [PATCH v3 4/5] x86: fix memory corruption in acpi_unmap

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Date:	Thu, 10 Apr 2014 19:14:20 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, imammedo@...hat.com, bp@...e.de,
	paul.gortmaker@...driver.com, JBeulich@...e.com, prarit@...hat.com,
	drjones@...hat.com, toshi.kani@...com, riel@...hat.com,
	gong.chen@...ux.intel.com, andi@...stfloor.org, lenb@...nel.org,
	rjw@...ysocki.net, linux-acpi@...r.kernel.org
Subject: [PATCH v3 4/5] x86: fix memory corruption in acpi_unmap_lsapic()

if during CPU hotplug master CPU failed to wake up AP
it set percpu x86_cpu_to_apicid to BAD_APICID=0xFFFF for AP.

However following attempt to unplug that CPU will lead to
out of bound write access to __apicid_to_node[] which is
32768 items long on x86_64 kernel.

So drop setting x86_cpu_to_apicid to BAD_APICID in do_boot_cpu()
and allow acpi_processor_remove()->acpi_unmap_lsapic() cleanly
remove CPU.

Signed-off-by: Igor Mammedov <imammedo@...hat.com>
---
 arch/x86/kernel/smpboot.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index e7c15d7..44903ad 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -821,8 +821,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 			udelay(100);
 			schedule();
 		}
-	} else {
-		per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID;
 	}
 
 	/* mark "stuck" area as not stuck */
-- 
1.7.1

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