Re: [PATCH 2/2] efi: Align unaccepted memory range to page boundary

[Kiryl Shutsemau <kas@kernel.org>]

On Mon, Feb 16, 2026 at 08:51:17AM -0600, Tom Lendacky wrote:
> On 2/13/26 09:48, Kiryl Shutsemau (Meta) wrote:
> > The accept_memory() and range_contains_unaccepted_memory() functions
> > employ a "guard page" logic to prevent crashes with load_unaligned_zeropad().
> > This logic extends the range to be accepted (or checked) by one unit_size
> > if the end of the range is aligned to a unit_size boundary.
> > 
> > However, if the caller passes a range that is not page-aligned, the
> > 'end' of the range might not be numerically aligned to unit_size, even
> > if it covers the last page of a unit. This causes the "if (!(end % unit_size))"
> > check to fail, skipping the necessary extension and leaving the next
> > unit unaccepted, which can lead to a kernel panic when accessed by
> > load_unaligned_zeropad().
> > 
> > Align the start address down and the size up to the nearest page
> > boundary before performing the unit_size alignment check. This ensures
> > that the guard unit is correctly added when the range effectively ends
> > on a unit boundary.
> > 
> > Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> > ---
> >  drivers/firmware/efi/unaccepted_memory.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
> > index c2c067eff634..9ddf3dedd514 100644
> > --- a/drivers/firmware/efi/unaccepted_memory.c
> > +++ b/drivers/firmware/efi/unaccepted_memory.c
> > @@ -35,14 +35,18 @@ void accept_memory(phys_addr_t start, unsigned long size)
> >  	struct efi_unaccepted_memory *unaccepted;
> >  	unsigned long range_start, range_end;
> >  	struct accept_range range, *entry;
> > -	phys_addr_t end = start + size;
> >  	unsigned long flags;
> > +	phys_addr_t end;
> >  	u64 unit_size;
> >  
> >  	unaccepted = efi_get_unaccepted_table();
> >  	if (!unaccepted)
> >  		return;
> >  
> > +	start = PAGE_ALIGN_DOWN(start);
> > +	size = PAGE_ALIGN(size);
> > +	end = start + size;
> 
> Should this really be:
> 
> 	end = PAGE_ALIGN(start + size);
> 	start = PAGE_ALIGN_DOWN(start);
> 
> ?

Doh! Yes, you are right.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov