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authorRusty Russell <rusty@rustcorp.com.au>2008-03-11 09:35:57 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-03-11 09:35:58 +1100
commit4357bd9453b81e0a41db1dec16e06d74256b7560 (patch)
tree4b23d512d6cbe26ac2b4a0dfaff7e415bd1dab7c /drivers/lguest/page_tables.c
parent3fabc55f34b72720e8a10aa442bd3415a211edb3 (diff)
lguest: Revert 1ce70c4fac3c3954bd48c035f448793867592bc0, fix real problem.
Ahmed managed to crash the Host in release_pgd(), which cannot be a Guest bug, and indeed it wasn't. The bug was that handing a 0 as the address of the toplevel page table being manipulated can cause the lookup code in find_pgdir() to return an uninitialized cache entry (we shadow up to 4 top level page tables for each Guest). Commit 37cc8d7f963ba2deec29c9b68716944516a3244f introduced this behaviour in the Guest, uncovering the bug. The patch which he submitted (which removed the /4 from the index calculation) simply ensured that these high-indexed entries hit the early exit path of guest_set_pmd(). But you get lots of segfaults in guest userspace as the PMDs aren't being updated. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'drivers/lguest/page_tables.c')
-rw-r--r--drivers/lguest/page_tables.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 275f23c2deb..a7f64a9d67e 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -391,7 +391,7 @@ static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
{
unsigned int i;
for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
- if (lg->pgdirs[i].gpgdir == pgtable)
+ if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable)
break;
return i;
}