linux-kernel - [PATCH 3.16 236/305] KVM: arm/arm64: Stop leaking vcpu pid references

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Message-ID: <lsq.1471110171.106206405@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "James Morse" <james.morse@....com>,
	"Christoffer Dall" <christoffer.dall@...aro.org>,
	"Marc Zyngier" <marc.zyngier@....com>
Subject: [PATCH 3.16 236/305] KVM: arm/arm64: Stop leaking vcpu pid references

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: James Morse <james.morse@....com>

commit 591d215afcc2f94e8e2c69a63c924c044677eb31 upstream.

kvm provides kvm_vcpu_uninit(), which amongst other things, releases the
last reference to the struct pid of the task that was last running the vcpu.

On arm64 built with CONFIG_DEBUG_KMEMLEAK, starting a guest with kvmtool,
then killing it with SIGKILL results (after some considerable time) in:
> cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff80007d5ea080 (size 128):
>  comm "lkvm", pid 2025, jiffies 4294942645 (age 1107.776s)
>  hex dump (first 32 bytes):
>    01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>  backtrace:
>    [<ffff8000001b30ec>] create_object+0xfc/0x278
>    [<ffff80000071da34>] kmemleak_alloc+0x34/0x70
>    [<ffff80000019fa2c>] kmem_cache_alloc+0x16c/0x1d8
>    [<ffff8000000d0474>] alloc_pid+0x34/0x4d0
>    [<ffff8000000b5674>] copy_process.isra.6+0x79c/0x1338
>    [<ffff8000000b633c>] _do_fork+0x74/0x320
>    [<ffff8000000b66b0>] SyS_clone+0x18/0x20
>    [<ffff800000085cb0>] el0_svc_naked+0x24/0x28
>    [<ffffffffffffffff>] 0xffffffffffffffff

On x86 kvm_vcpu_uninit() is called on the path from kvm_arch_destroy_vm(),
on arm no equivalent call is made. Add the call to kvm_arch_vcpu_free().

Signed-off-by: James Morse <james.morse@....com>
Fixes: 749cf76c5a36 ("KVM: ARM: Initial skeleton to compile KVM support")
Acked-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/kvm/arm.c | 1 +
 1 file changed, 1 insertion(+)

--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -258,6 +258,7 @@ void kvm_arch_vcpu_free(struct kvm_vcpu
 {
 	kvm_mmu_free_memory_caches(vcpu);
 	kvm_timer_vcpu_terminate(vcpu);
+	kvm_vcpu_uninit(vcpu);
 	kmem_cache_free(kvm_vcpu_cache, vcpu);
 }