From: Rusty Russell Date: Tue, 11 Mar 2008 14:35:57 +0000 (-0500) Subject: lguest: Revert 1ce70c4fac3c3954bd48c035f448793867592bc0, fix real problem. X-Git-Tag: v2.6.25-rc6~49^2~1 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=4357bd9453b81e0a41db1dec16e06d74256b7560;p=linux-2.6-omap-h63xx.git 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 --- diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c index 9c27c104d83..a104c532ff7 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 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; }