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References: <20200305183939.256241-1-davidgow@google.com>
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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Tue, 10 Mar 2020 14:24:22 -0700
Message-ID: <CAFd5g45XJLXYfXB-FJhFYnBYUdqM4ztC=p=Akj3+GbHXfHxzgQ@mail.gmail.com>
Subject: Re: [PATCH] um: Fix overlapping ELF segments when statically linked
To:     David Gow <davidgow@google.com>
Cc:     Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Patricia Alfonso <trishalfonso@google.com>,
        linux-um <linux-um@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Mar 5, 2020 at 10:39 AM David Gow <davidgow@google.com> wrote:
>
> When statically linked, the .text section in UML kernels is not page
> aligned, causing it to share a page with the executable headers. As
> .text and the executable headers have different permissions, this causes
> the kernel to wish to map the same page twice (once as headers with r--
> permissions, once as .text with r-x permissions), causing a segfault,
> and a nasty message printed to the host kernel's dmesg:
>
> "Uhuuh, elf segment at 0000000060000000 requested but the memory is
> mapped already"
>
> By aligning the .text to a page boundary (as in the dynamically linked
> version in dyn.lds.S), there is no such overlap, and the kernel runs
> correctly.
>
> Signed-off-by: David Gow <davidgow@google.com>

I can confirm that I am seeing this problem as well. (I know we run
the same Linux distro; nevertheless, this is a real problem for some
population of users.)

Reviewed-by: Brendan Higgins <brendanhiggins@google.com>