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SubjectRe: [PATCH v2 1/5] x86/mm/pageattr: Ensure cpa->pfn only contains page frame numbers

* Matt Fleming <matt@codeblueprint.co.uk> wrote:

> > > + npages = (_end - _text) >> PAGE_SHIFT;
> >
> > You really need to PFN_ALIGN _end and _text. Has been wrong in the
> > existing code as well.
>
> Hmm... very good point.

So I think we should instead guarantee that _end and _text are page aligned.

_text is already page aligned:

SECTIONS
{
#ifdef CONFIG_X86_32
. = LOAD_OFFSET + LOAD_PHYSICAL_ADDR;
phys_startup_32 = startup_32 - LOAD_OFFSET;
#else
. = __START_KERNEL;
phys_startup_64 = startup_64 - LOAD_OFFSET;
#endif

/* Text and read-only data */
.text : AT(ADDR(.text) - LOAD_OFFSET) {
_text = .;

The reason for aligning _end as well is that we already page-align the BSS and BRK
sections of the kernel and its various section boundary symbols:

/* BSS */
. = ALIGN(PAGE_SIZE);
.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
__bss_start = .;
*(.bss..page_aligned)
*(.bss)
. = ALIGN(PAGE_SIZE);
__bss_stop = .;
}

. = ALIGN(PAGE_SIZE);
.brk : AT(ADDR(.brk) - LOAD_OFFSET) {
__brk_base = .;
. += 64 * 1024; /* 64k alignment slop space */
*(.brk_reservation) /* areas brk users have reserved */
__brk_limit = .;
}

_end = .;

STABS_DEBUG
DWARF_DEBUG

_end is the only odd one out, so we should align it as well - because it's easy to
make such pfn conversion bugs.

This will also make it easier to mark STABS_DEBUG and DWARF_DEBUG as read-only,
which they should fundamentally be I think. Alternatively they could be moved to
the read-only section - at which point _end becomes page aligned 'for free'.

Thanks,

Ingo


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