| Message ID | fb3254e25e38790c538cca0f46c4a7a714c77ddf.1468270393.git.luto@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 11 Jul 2016 13:53:36 -0700, Andy Lutomirski said: > 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 <luto@kernel.org> > --- > arch/x86/mm/pageattr.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) I just bisected a failure to boot down to this patch. On my Dell Latitude laptop, it results in the kernel being loaded and then just basically sitting there dead in the water - as far as I can tell, it dies before the kernel ever gets going far enough to do any console I/O (even with ignore_loglevel). Nothing in /sys/fs/pstore either. I admit not understanding the VM code at all, so I don't have a clue *why* this causes indigestion... CPU is an Intel Core i5-3340M in case that matters....
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 7a1f7bbf4105..6088aa03de63 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -1104,8 +1104,6 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr) pud = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK); if (!pud) return -1; - - set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE)); } pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr); @@ -1113,11 +1111,16 @@ 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; } + if (pud) + set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE)); + cpa->numpages = ret; return 0; }
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 <luto@kernel.org> --- arch/x86/mm/pageattr.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)