Date: Wed, 5 Jul 2017 14:30:38 -0500 From: Alan Cox <alc@rice.edu> To: Guy Yur <guyyur@gmail.com>, alc@freebsd.org Cc: freebsd-current <freebsd-current@freebsd.org>, kib@freebsd.org, Sean Bruno <sbruno@freebsd.org> Subject: Re: emulators/qemu-user-static needs MAP_GUARD support Message-ID: <fc06e92f-9d0d-1c6e-25ee-f8d0408d3b16@rice.edu> In-Reply-To: <CAC67Hz91TXZS15qKnwNbpJwDZTL3eH%2BjY-=uQP-ca_1mZvJRug@mail.gmail.com> References: <CAC67Hz91TXZS15qKnwNbpJwDZTL3eH%2BjY-=uQP-ca_1mZvJRug@mail.gmail.com>
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On 07/05/2017 13:47, Guy Yur wrote: > Hi Alan, > > On 1 July 2017 at 23:07, Alan Cox <alan.l.cox@gmail.com> wrote: >> On Sat, Jul 1, 2017 at 2:46 PM, Guy Yur <guyyur@gmail.com> wrote: >>> Hi, >>> >>> I tried to run armv6 /bin/sh in a chroot on an >>> amd64 host using qemu-arm-static. >>> It failed on invalid argument to mmap. >>> >>> # cp /usr/local/bin/qemu-arm-static /chroots/armv6/root/ >>> # chroot /chroots/armv6 /root/qemu-arm-static /bin/sh >>> /lib/libedit.so.7: mmap of entire address space failed: Invalid argument >>> >>> ... snipped >>> >> MAP_ANON should not be passed to mmap(2) at the same time as MAP_GUARD. >> Passing MAP_FIXED at the same time is okay. >> > The problem is definitely in qemu user mode mmap emulation code. > https://github.com/seanbruno/qemu-bsd-user/blob/bsd-user/bsd-user/mmap.c#L464 > > qemu adds MAP_FIXED | MAP_ANONYMOUS if MAP_FIXED is not > set in flags when the emulated mmap call is done. > So rtld-elf passes MAP_GUARD and the kernel receives MAP_GUARD > and MAP_ANON and rejects the call. > > Do you know if the MAP_ANONYMOUS is needed in the call? Try removing the MAP_ANON (or MAP_ANONYMOUS). Adding MAP_FIXED should not imply the addition of MAP_ANON. > I am currently using a workaround patch to convert > MAP_GUARD to MAP_PRIVATE | MAP_ANON | MAP_NOCORE > (like rtld-elf does if OS version doesn't support MAP_GUARD). > https://github.com/guyyur/freebsd-ports_patches/blob/master/emulators_qemu-sbruno__MAP_GUARD_workaround.patch > With the patch qemu-arm-static is working. > > I would prefer using a better fix that retains the MAP_GUARD protections. > > Thanks, > Guy >
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