On Thu, Jul 26, 2018 at 08:10:42AM +0000, Dmitry Malkin wrote:
>
>
> On 07/25/2018 11:21 PM, Kirill A. Shutemov wrote:
> > On Wed, Jul 25, 2018 at 05:26:02PM +0000, Dmitry Malkin wrote:
> > > there may be some other reasons which may cause undefined behavior (reboot
> > > for example):
> > >
> > > in arch/x86/boot/compressed/pgtable_64.c in function paging_prepare():
> > >
> > > 1. structure "paging_config" allocated on stack without setting default
> > > value for flag "l5_required":
> > > > > struct paging_config paging_config = {};
> > > l5_required is set only if CONFIG_X86_5LEVEL is defined
> > Hm? C99 initializer zeros the structure.
> https://elixir.bootlin.com/linux/latest/source/Makefile#L366
> Here I only see std=gnu89.
gnu89 support C99-style initializers. The syntax above would clear fields
that not initialized explicitly, in this case all of them.
> > > 2. reading from memory which may be reserved in case of EFI systems:
> > > > > ebda_start = *(unsigned short *)0x40e << 4;
> > > > > bios_start = *(unsigned short *)0x413 << 10;
> > > Also, on EFI system without CSM it will results in all zeros. Which will
> > > place trampoline_start to 0x9d000. And it also may be reserved memory. In
> > > fact I have such system and it is causes instant reboot (when code starts
> > > copying to "trampoline_start").
> > Could you show dmesg from such system?
> Sure, here it is (please note than not both pages are reserved but only
> second one: 0x9e000-0x9ffff):
Well. That's bad.
I don't see much options but parse e820 in decompression code. I hoped to
avoid this.
Let me see what I can do there.
--
Kirill A. Shutemov
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