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Re: [PATCH v2] linux-user: Adjust pgd_find_hole_fallback result with gue
From: |
Laurent Vivier |
Subject: |
Re: [PATCH v2] linux-user: Adjust pgd_find_hole_fallback result with guest_loaddr |
Date: |
Tue, 9 Mar 2021 22:49:51 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 |
Le 06/03/2021 à 10:33, Ivan A. Melnikov a écrit :
> While pgd_find_hole_fallback returns the beginning of the
> hole found, pgb_find_hole returns guest_base, which
> is somewhat different as the binary qemu-user is loading
> usually have non-zero load address.
>
> Failing to take that into account leads to random crashes
> if the hole is "just big enough", but not bigger:
> in that case, important mappings (e.g. parts of qemu-user
> itself) may be replaced with the binary we are loading
> (e.g. guest elf interpreter).
>
> Downstream issue (in Russian): https://bugzilla.altlinux.org/39141
> Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>
> ---
> linux-user/elfload.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index bab4237e90..58281e00f8 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2259,7 +2259,8 @@ static uintptr_t pgb_find_hole(uintptr_t guest_loaddr,
> uintptr_t guest_size,
> brk = (uintptr_t)sbrk(0);
>
> if (!maps) {
> - return pgd_find_hole_fallback(guest_size, brk, align, offset);
> + ret = pgd_find_hole_fallback(guest_size, brk, align, offset);
> + return (ret == (uintptr_t) -1) ? -1 : (ret - guest_loaddr);
You don't want the uintptr_t as ret is intptr_t
> }
>
> /* The first hole is before the first map entry. */
>
I've already added the patch from Vincent Fazio to fix the problem.
https://github.com/vivier/qemu/commit/5112f50d6e889a2a1098fb2a67a0851641c350f4
It will be in my next pull request.
Thanks,
Laurent