linux-kernel - Re: [PATCH v4] kmemleak: survive in a low-memory situation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 27 Mar 2019 09:05:31 -0400
From:   Qian Cai <cai@....pw>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, catalin.marinas@....com, cl@...ux.com,
        willy@...radead.org, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation

On 3/27/19 7:44 AM, Michal Hocko wrote> What? Normal spin lock implementation
doesn't disable interrupts. So
> either I misunderstand what you are saying or you seem to be confused.
> the thing is that in_atomic relies on preempt_count to work properly and
> if you have CONFIG_PREEMPT_COUNT=n then you simply never know whether
> preemption is disabled so you do not know that a spin_lock is held.
> irqs_disabled on the other hand checks whether arch specific flag for
> IRQs handling is set (or cleared). So you would only catch irq safe spin
> locks with the above check.

Exactly, because kmemleak_alloc() is only called in a few call sites, slab
allocation, neigh_hash_alloc(), alloc_page_ext(), sg_kmalloc(),
early_amd_iommu_init() and blk_mq_alloc_rqs(), my review does not yield any of
those holding irq unsafe spinlocks.

Could future code changes suddenly call kmemleak_alloc() with a irq unsafe
spinlock held? Always possible, but it is unlikely to happen. I could put some
comments on kmemleak_alloc() about this though.