Messages in this thread | | | From | Ard Biesheuvel <> | Date | Thu, 27 Feb 2020 16:21:32 +0100 | Subject | Re: [PATCH v2 1/1] x86/boot/compressed: Fix reloading of GDTR post-relocation |
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On Thu, 27 Feb 2020 at 16:16, Arvind Sankar <nivedita@alum.mit.edu> wrote: > > On Thu, Feb 27, 2020 at 09:12:29AM +0100, Ingo Molnar wrote: > > > > * Arvind Sankar <nivedita@alum.mit.edu> wrote: > > > > > Commit ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main") > > > introduced GDT setup into the 32-bit kernel's startup_32, and reloads > > > the GDTR after relocating the kernel for paranoia's sake. > > > > > > Commit 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of > > > the buffer") introduced a similar GDTR reload in the 64-bit kernel. > > > > > > The GDTR is adjusted by init_size - _end, however this may not be the > > > correct offset to apply if the kernel was loaded at a misaligned address > > > or below LOAD_PHYSICAL_ADDR, as in that case the decompression buffer > > > has an additional offset from the original load address. > > > > > > This should never happen for a conformant bootloader, but we're being > > > paranoid anyway, so just store the new GDT address in there instead of > > > adding any offsets, which is simpler as well. > > > > > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> > > > Fixes: ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main") > > > Fixes: 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of the buffer") > > > > Have you or anyone else observed this condition practice, or have a > > suspicion that this could happen - or is this a mostly theoretical > > concern? > > > > Thanks, > > > > Ingo > > Right now it's a theoretical concern. > > I'm working on another patch, to tell the EFI firmware PE loader what > the kernel's preferred address is, so that we can avoid having to > relocate the kernel in the EFI stub in most cases (ie if the PE loader > manages to load us at that address). With those changes, the required > adjustment won't be init_size - _end any more, and while fixing it up > there, I noticed that it could already be the case that the required > adjustment is different. >
Do you mean setting the image address in the PE/COFF header to the preferred address?
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