diff options
| author | Rusty Russell | 2008-03-11 09:35:57 -0500 |
|---|---|---|
| committer | Rusty Russell | 2008-03-11 09:35:58 +1100 |
| commit | 4357bd9453b81e0a41db1dec16e06d74256b7560 (patch) | |
| tree | 4b23d512d6cbe26ac2b4a0dfaff7e415bd1dab7c /arch/x86 | |
| parent | 3fabc55f34b72720e8a10aa442bd3415a211edb3 (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 'arch/x86')
| -rw-r--r-- | arch/x86/lguest/boot.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c index 9c27c104d83c..a104c532ff70 100644 --- a/arch/x86/lguest/boot.c +++ b/arch/x86/lguest/boot.c @@ -480,7 +480,7 @@ static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval) { *pmdp = pmdval; lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK, - (__pa(pmdp)&(PAGE_SIZE-1)), 0); + (__pa(pmdp)&(PAGE_SIZE-1))/4, 0); } /* There are a couple of legacy places where the kernel sets a PTE, but we |