On 07/21/2016 09:43 PM, Valdis.Kletnieks@xxxxxx wrote:
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@xxxxxxxxxx>
---
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....
How much memory do you have and what's your config? My code is
obviously buggy, but I'm wondering why neither I nor the 0day bot caught
this.
The attached patch is compile-tested only. (Even Thunderbird doesn't
want to send non-flowed text right now, sigh.)
--Andy
>From 6589ddf69a1369e1ecb95f0af489d90b980e256e Mon Sep 17 00:00:00 2001
Message-Id: <6589ddf69a1369e1ecb95f0af489d90b980e256e.1469165371.git.luto@xxxxxxxxxx>
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Thu, 21 Jul 2016 22:22:02 -0700
Subject: [PATCH] x86/mm: Fix populate_pgd()
I make an obvious error in populate_pgd() -- it would fail to correctly
populate the page tables when it allocated a new pud page.
Fixes: 360cb4d15567 ("x86/mm/cpa: In populate_pgd(), don't set the PGD entry until it's populated")
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/mm/pageattr.c | 28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 26c93c6e04a0..5ee7d1c794a4 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -984,8 +984,8 @@ static int populate_pmd(struct cpa_data *cpa,
return num_pages;
}
-static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
- pgprot_t pgprot)
+static int populate_pud(struct cpa_data *cpa, unsigned long start,
+ pud_t *pud_page, pgprot_t pgprot)
{
pud_t *pud;
unsigned long end;
@@ -1006,7 +1006,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
cur_pages = (pre_end - start) >> PAGE_SHIFT;
cur_pages = min_t(int, (int)cpa->numpages, cur_pages);
- pud = pud_offset(pgd, start);
+ pud = pud_page + pud_index(start);
/*
* Need a PMD page?
@@ -1027,7 +1027,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
if (cpa->numpages == cur_pages)
return cur_pages;
- pud = pud_offset(pgd, start);
+ pud = pud_page + pud_index(start);
pud_pgprot = pgprot_4k_2_large(pgprot);
/*
@@ -1047,7 +1047,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
if (start < end) {
int tmp;
- pud = pud_offset(pgd, start);
+ pud = pud_page + pud_index(start);
if (pud_none(*pud))
if (alloc_pmd_page(pud))
return -1;
@@ -1069,7 +1069,7 @@ static int populate_pud(struct cpa_data *cpa, unsigned long start, pgd_t *pgd,
static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
{
pgprot_t pgprot = __pgprot(_KERNPG_TABLE);
- pud_t *pud = NULL; /* shut up gcc */
+ pud_t *pud_page = NULL; /* shut up gcc */
pgd_t *pgd_entry;
int ret;
@@ -1079,25 +1079,27 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
* Allocate a PUD page and hand it down for mapping.
*/
if (pgd_none(*pgd_entry)) {
- pud = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
- if (!pud)
+ pud_page = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
+ if (!pud_page)
return -1;
}
pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);
pgprot_val(pgprot) |= pgprot_val(cpa->mask_set);
- ret = populate_pud(cpa, addr, pgd_entry, pgprot);
+ ret = populate_pud(cpa, addr,
+ pud_page ?: (pud_t *)pgd_page_vaddr(*pgd_entry),
+ pgprot);
if (ret < 0) {
- if (pud)
- free_page((unsigned long)pud);
+ if (pud_page)
+ free_page((unsigned long)pud_page);
unmap_pud_range(pgd_entry, addr,
addr + (cpa->numpages << PAGE_SHIFT));
return ret;
}
- if (pud)
- set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
+ if (pud_page)
+ set_pgd(pgd_entry, __pgd(__pa(pud_page) | _KERNPG_TABLE));
cpa->numpages = ret;
return 0;
--
2.7.4
