On Sun, Jun 26, 2016 at 02:55:26PM -0700, Andy Lutomirski wrote:
> This avoids pointless races in which another CPU or task might see a
> partially populated global pgd entry. These races should normally
> be harmless, but, if another CPU propagates the entry via
> vmalloc_fault and then populate_pgd fails (due to memory allocation
> failure, for example), this prevents a use-after-free of the pgd
> entry.
>
> Signed-off-by: Andy Lutomirski <l...@kernel.org>
> ---
> arch/x86/mm/pageattr.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 7a1f7bbf4105..6a8026918bf6 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -1113,7 +1113,9 @@ static int populate_pgd(struct cpa_data *cpa, unsigned
> long addr)
>
> ret = populate_pud(cpa, addr, pgd_entry, pgprot);
> if (ret < 0) {
> - unmap_pgd_range(cpa->pgd, addr,
> + if (pud)
> + free_page((unsigned long)pud);
> + unmap_pud_range(pgd_entry, addr,
> addr + (cpa->numpages << PAGE_SHIFT));
> return ret;
> }
> --
So something's amiss here. Subject says:
"x86/cpa: In populate_pgd, don't set the pgd entry until it's populated"
but you haven't moved
set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
after populate_pud() succeeds... Which is a good catch but your patch
should do it too. :-)
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
