linux-kernel - Re: [PATCH v4] mm/vmalloc: randomize vmalloc() allocations

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Message-ID: <ba975607-9493-c78c-bbd8-6a85573114d1@gmail.com>
Date:   Mon, 15 Mar 2021 13:45:18 +0200
From:   Topi Miettinen <toiwoton@...il.com>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     linux-hardening@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v4] mm/vmalloc: randomize vmalloc() allocations

On 14.3.2021 19.23, Uladzislau Rezki wrote:
> Also, using vmaloc test driver i can trigger a kernel BUG:
> 
> <snip>
> [   24.627577] kernel BUG at mm/vmalloc.c:1272!

It seems that most tests indeed fail. Perhaps the vmalloc subsystem 
isn't very robust in face of fragmented virtual memory. What could be 
done to fix that?

In this patch, I could retry __alloc_vmap_area() with the whole region 
after failure of both [random, vend] and [vstart, random] but I'm not 
sure that would help much. Worth a try of course.

By the way, some of the tests in test_vmalloc.c don't check for 
vmalloc() failure, for example in full_fit_alloc_test().

-Topi