On Tue, Jun 28, 2016 at 11:48 AM, Borislav Petkov <[email protected]> wrote: > 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 <[email protected]> >> --- >> 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. :-)
Good catch. I'll fix this in the next version. --Andy
