On Thu, May 17, 2018 at 09:01:06AM +0200, Sascha Hauer wrote:
> On Thu, May 17, 2018 at 06:52:10AM +0200, Oleksij Rempel wrote:
> > Am 16.05.2018 um 23:34 schrieb Peter Mamonov:
> > > Hi!
> > >
> > > On Wed, May 16, 2018 at 06:42:27PM +0200, Oleksij Rempel wrote:
> > >> From: Antony Pavlov <antonynpavlov@xxxxxxxxx>
> > >>
> > >> +int kexec_load_bootm_data(struct image_data *data)
> > >> +{
> > >> + int ret;
> > >> + struct kexec_info info;
> > >> + char *cmdline;
> > >> + const char *t;
> > >> + size_t tlen;
> > >> + size_t fsize;
> > >> + char initrd_cmdline[40];
> > >> + int padded = 0;
> > >> +
> > >> + memset(&info, 0, sizeof(info));
> > >> +
> > >> + initrd_cmdline[0] = 0;
> > >> +
> > >> + ret = kexec_load_one_file(&info, data->os_file);
> > >> + if (IS_ERR_VALUE(ret)) {
> > >> + pr_err("Cannot load %s\n", data->os_file);
> > >> + return ret;
> > >> + }
> > >
> > > There is a potential problem here, which I actually hit some time ago. The
> > > following code places kernel arguments right after os image. This is perfectly
> > > fine in case of vmlinuX. However, if one boots a vmlinuZ image, there is no
> > > easily available knowledge of where the decompressed image will reside. In my
> > > case vmlinux' BSS overlapped with DTB and kernel cmdline segments and was
> > > zeroed at linux startup. This was fixed by adding an empty 4k segment at 128M,
> > > so further segments were allocated beyond 128M, far enough from the kernel
> > > lair:
> > >
> > > + /* FIXME: allocate 4k segment @ 0x8000000 (128M), so further
> > > + * segments will be allocated beyond this address. This prevents
> > > + * kernel parameters from being overwritten by the kernel startup code.
> > > + */
> > > + add_segment(&info, (void *)CKSEG0ADDR(0), 4 << 10, 0x8000000, 4 << 10);
> > >
> > > However this is an ad-hoc solution and, probably, find_unused_base() may take
> > > care of such cases.
> >
> > Yes, correct. This and some other issues would be fixed by porting this
> > part of the code to bootm_load_devicetree() + find_unused_base(). Since
> > my time budget is on the limit, I would prefer to mainline current state
> > of the code ("works for me" TM) and provide platform for testing and
> > cooperation.
>
> Can we at least detect that the image is a compressed one and bail out
> with an error? It would be a pity when someone else has to figure out
> this bug the hard way now that we already know that it exists.
I suggest to print a warning message, containing relevant addresses. Something
like this:
ACHTUNG: booting vmlinuZ image. Beware of overlaps of kernel arguments
and vmlinuX sections. List of kernel arguments:
cmdline @ XXXXXXXX-XXXXXXXX
dtb @ XXXXXXXX-XXXXXXXX
However I'm not sure if it is possible to distinguish vmlinuz from vmlinux
reliably, since both are just ELFs, though vmlinuz has only one section.
Moreover, I guess this issue applies to any form of compressed OS image, not
only vmlinuz. So, probably linux should take care about its arguments in
arch/mips/boot/compressed/head.S.
Regards,
Peter
>
> Sascha
>
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