Re: [PATCH 01/12] KVM: MMU: Fix ubsan warnings
From: Mike Krinkin
Date: Wed Feb 24 2016 - 08:42:59 EST
Could you also merge a fix for the following ubsan warning (i
reported this one too, but it attracted a bit less attention):
[ 168.791851] ================================================================================
[ 168.791862] UBSAN: Undefined behaviour in arch/x86/kvm/paging_tmpl.h:252:15
[ 168.791866] index 4 is out of range for type 'u64 [4]'
[ 168.791871] CPU: 0 PID: 2950 Comm: qemu-system-x86 Tainted: G O L 4.5.0-rc5-next-20160222 #7
[ 168.791873] Hardware name: LENOVO 23205NG/23205NG, BIOS G2ET95WW (2.55 ) 07/09/2013
[ 168.791876] 0000000000000000 ffff8801cfcaf208 ffffffff81c9f780 0000000041b58ab3
[ 168.791882] ffffffff82eb2cc1 ffffffff81c9f6b4 ffff8801cfcaf230 ffff8801cfcaf1e0
[ 168.791886] 0000000000000004 0000000000000001 0000000000000000 ffffffffa1981600
[ 168.791891] Call Trace:
[ 168.791899] [<ffffffff81c9f780>] dump_stack+0xcc/0x12c
[ 168.791904] [<ffffffff81c9f6b4>] ? _atomic_dec_and_lock+0xc4/0xc4
[ 168.791910] [<ffffffff81da9e81>] ubsan_epilogue+0xd/0x8a
[ 168.791914] [<ffffffff81daafa2>] __ubsan_handle_out_of_bounds+0x15c/0x1a3
[ 168.791918] [<ffffffff81daae46>] ? __ubsan_handle_shift_out_of_bounds+0x2bd/0x2bd
[ 168.791922] [<ffffffff811287ef>] ? get_user_pages_fast+0x2bf/0x360
[ 168.791954] [<ffffffffa1794050>] ? kvm_largepages_enabled+0x30/0x30 [kvm]
[ 168.791958] [<ffffffff81128530>] ? __get_user_pages_fast+0x360/0x360
[ 168.791987] [<ffffffffa181b818>] paging64_walk_addr_generic+0x1b28/0x2600 [kvm]
[ 168.792014] [<ffffffffa1819cf0>] ? init_kvm_mmu+0x1100/0x1100 [kvm]
[ 168.792019] [<ffffffff8129e350>] ? debug_check_no_locks_freed+0x350/0x350
[ 168.792044] [<ffffffffa1819cf0>] ? init_kvm_mmu+0x1100/0x1100 [kvm]
[ 168.792076] [<ffffffffa181c36d>] paging64_gva_to_gpa+0x7d/0x110 [kvm]
[ 168.792121] [<ffffffffa181c2f0>] ? paging64_walk_addr_generic+0x2600/0x2600 [kvm]
[ 168.792130] [<ffffffff812e848b>] ? debug_lockdep_rcu_enabled+0x7b/0x90
[ 168.792178] [<ffffffffa17d9a4a>] emulator_read_write_onepage+0x27a/0x1150 [kvm]
[ 168.792208] [<ffffffffa1794d44>] ? __kvm_read_guest_page+0x54/0x70 [kvm]
[ 168.792234] [<ffffffffa17d97d0>] ? kvm_task_switch+0x160/0x160 [kvm]
[ 168.792238] [<ffffffff812e848b>] ? debug_lockdep_rcu_enabled+0x7b/0x90
[ 168.792263] [<ffffffffa17daa07>] emulator_read_write+0xe7/0x6d0 [kvm]
[ 168.792290] [<ffffffffa183b620>] ? em_cr_write+0x230/0x230 [kvm]
[ 168.792314] [<ffffffffa17db005>] emulator_write_emulated+0x15/0x20 [kvm]
[ 168.792340] [<ffffffffa18465f8>] segmented_write+0xf8/0x130 [kvm]
[ 168.792367] [<ffffffffa1846500>] ? em_lgdt+0x20/0x20 [kvm]
[ 168.792374] [<ffffffffa14db512>] ? vmx_read_guest_seg_ar+0x42/0x1e0 [kvm_intel]
[ 168.792400] [<ffffffffa1846d82>] writeback+0x3f2/0x700 [kvm]
[ 168.792424] [<ffffffffa1846990>] ? em_sidt+0xa0/0xa0 [kvm]
[ 168.792449] [<ffffffffa185554d>] ? x86_decode_insn+0x1b3d/0x4f70 [kvm]
[ 168.792474] [<ffffffffa1859032>] x86_emulate_insn+0x572/0x3010 [kvm]
[ 168.792499] [<ffffffffa17e71dd>] x86_emulate_instruction+0x3bd/0x2110 [kvm]
[ 168.792524] [<ffffffffa17e6e20>] ? reexecute_instruction.part.110+0x2e0/0x2e0 [kvm]
[ 168.792532] [<ffffffffa14e9a81>] handle_ept_misconfig+0x61/0x460 [kvm_intel]
[ 168.792539] [<ffffffffa14e9a20>] ? handle_pause+0x450/0x450 [kvm_intel]
[ 168.792546] [<ffffffffa15130ea>] vmx_handle_exit+0xd6a/0x1ad0 [kvm_intel]
[ 168.792572] [<ffffffffa17f6a6c>] ? kvm_arch_vcpu_ioctl_run+0xbdc/0x6090 [kvm]
[ 168.792597] [<ffffffffa17f6bcd>] kvm_arch_vcpu_ioctl_run+0xd3d/0x6090 [kvm]
[ 168.792621] [<ffffffffa17f6a6c>] ? kvm_arch_vcpu_ioctl_run+0xbdc/0x6090 [kvm]
[ 168.792627] [<ffffffff8293b530>] ? __ww_mutex_lock_interruptible+0x1630/0x1630
[ 168.792651] [<ffffffffa17f5e90>] ? kvm_arch_vcpu_runnable+0x4f0/0x4f0 [kvm]
[ 168.792656] [<ffffffff811eeb30>] ? preempt_notifier_unregister+0x190/0x190
[ 168.792681] [<ffffffffa17e0447>] ? kvm_arch_vcpu_load+0x127/0x650 [kvm]
[ 168.792704] [<ffffffffa178e9a3>] kvm_vcpu_ioctl+0x553/0xda0 [kvm]
[ 168.792727] [<ffffffffa178e450>] ? vcpu_put+0x40/0x40 [kvm]
[ 168.792732] [<ffffffff8129e350>] ? debug_check_no_locks_freed+0x350/0x350
[ 168.792735] [<ffffffff82946087>] ? _raw_spin_unlock+0x27/0x40
[ 168.792740] [<ffffffff8163a943>] ? handle_mm_fault+0x1673/0x2e40
[ 168.792744] [<ffffffff8129daa8>] ? trace_hardirqs_on_caller+0x478/0x6c0
[ 168.792747] [<ffffffff8129dcfd>] ? trace_hardirqs_on+0xd/0x10
[ 168.792751] [<ffffffff812e848b>] ? debug_lockdep_rcu_enabled+0x7b/0x90
[ 168.792756] [<ffffffff81725a80>] do_vfs_ioctl+0x1b0/0x12b0
[ 168.792759] [<ffffffff817258d0>] ? ioctl_preallocate+0x210/0x210
[ 168.792763] [<ffffffff8174aef3>] ? __fget+0x273/0x4a0
[ 168.792766] [<ffffffff8174acd0>] ? __fget+0x50/0x4a0
[ 168.792770] [<ffffffff8174b1f6>] ? __fget_light+0x96/0x2b0
[ 168.792773] [<ffffffff81726bf9>] SyS_ioctl+0x79/0x90
[ 168.792777] [<ffffffff82946880>] entry_SYSCALL_64_fastpath+0x23/0xc1
[ 168.792780] ================================================================================
This seems to be a typo, and the following fix solves problem for me:
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 6c9fed9..2ce4f05 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -249,7 +249,7 @@ static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
return ret;
kvm_vcpu_mark_page_dirty(vcpu, table_gfn);
- walker->ptes[level] = pte;
+ walker->ptes[level - 1] = pte;
}
return 0;
}
On Wed, Feb 24, 2016 at 02:17:42PM +0100, Paolo Bonzini wrote:
> kvm_mmu_pages_init is doing some really yucky stuff. It is setting
> up a sentinel for mmu_page_clear_parents; however, because of a) the
> way levels are numbered starting from 1 and b) the way mmu_page_path
> sizes its arrays with PT64_ROOT_LEVEL-1 elements, the access can be
> out of bounds. This is harmless because the code overwrites up to the
> first two elements of parents->idx and these are initialized, and
> because the sentinel is not needed in this case---mmu_page_clear_parents
> exits anyway when it gets to the end of the array. However ubsan
> complains, and everyone else should too.
>
> This fix does three things. First it makes the mmu_page_path arrays
> PT64_ROOT_LEVEL elements in size, so that we can write to them without
> checking the level in advance. Second it disintegrates kvm_mmu_pages_init
> between mmu_unsync_walk (to reset the struct kvm_mmu_pages) and
> for_each_sp (to place the NULL sentinel at the end of the current path).
> This is okay because the mmu_page_path is only used in
> mmu_pages_clear_parents; mmu_pages_clear_parents itself is called within
> a for_each_sp iterator, and hence always after a call to mmu_pages_next.
> Third it changes mmu_pages_clear_parents to just use the sentinel to
> stop iteration, without checking the bounds on level.
>
> Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Reported-by: Mike Krinkin <krinkin.m.u@xxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 57 +++++++++++++++++++++++++++++++-----------------------
> 1 file changed, 33 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 07f4c26a10d3..4dee855897cf 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1843,6 +1843,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
> static int mmu_unsync_walk(struct kvm_mmu_page *sp,
> struct kvm_mmu_pages *pvec)
> {
> + pvec->nr = 0;
> if (!sp->unsync_children)
> return 0;
>
> @@ -1956,13 +1957,12 @@ static void kvm_sync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
> }
>
> struct mmu_page_path {
> - struct kvm_mmu_page *parent[PT64_ROOT_LEVEL-1];
> - unsigned int idx[PT64_ROOT_LEVEL-1];
> + struct kvm_mmu_page *parent[PT64_ROOT_LEVEL];
> + unsigned int idx[PT64_ROOT_LEVEL];
> };
>
> #define for_each_sp(pvec, sp, parents, i) \
> - for (i = mmu_pages_next(&pvec, &parents, -1), \
> - sp = pvec.page[i].sp; \
> + for (i = mmu_pages_first(&pvec, &parents); \
> i < pvec.nr && ({ sp = pvec.page[i].sp; 1;}); \
> i = mmu_pages_next(&pvec, &parents, i))
>
> @@ -1974,19 +1974,41 @@ static int mmu_pages_next(struct kvm_mmu_pages *pvec,
>
> for (n = i+1; n < pvec->nr; n++) {
> struct kvm_mmu_page *sp = pvec->page[n].sp;
> + unsigned idx = pvec->page[n].idx;
> + int level = sp->role.level;
>
> - if (sp->role.level == PT_PAGE_TABLE_LEVEL) {
> - parents->idx[0] = pvec->page[n].idx;
> - return n;
> - }
> + parents->idx[level-1] = idx;
> + if (level == PT_PAGE_TABLE_LEVEL)
> + break;
>
> - parents->parent[sp->role.level-2] = sp;
> - parents->idx[sp->role.level-1] = pvec->page[n].idx;
> + parents->parent[level-2] = sp;
> }
>
> return n;
> }
>
> +static int mmu_pages_first(struct kvm_mmu_pages *pvec,
> + struct mmu_page_path *parents)
> +{
> + struct kvm_mmu_page *sp;
> + int level;
> +
> + if (pvec->nr == 0)
> + return 0;
> +
> + sp = pvec->page[0].sp;
> + level = sp->role.level;
> + WARN_ON(level == PT_PAGE_TABLE_LEVEL);
> +
> + parents->parent[level-2] = sp;
> +
> + /* Also set up a sentinel. Further entries in pvec are all
> + * children of sp, so this element is never overwritten.
> + */
> + parents->parent[level-1] = NULL;
> + return mmu_pages_next(pvec, parents, 0);
> +}
> +
> static void mmu_pages_clear_parents(struct mmu_page_path *parents)
> {
> struct kvm_mmu_page *sp;
> @@ -1994,22 +2016,13 @@ static void mmu_pages_clear_parents(struct mmu_page_path *parents)
>
> do {
> unsigned int idx = parents->idx[level];
> -
> sp = parents->parent[level];
> if (!sp)
> return;
>
> clear_unsync_child_bit(sp, idx);
> level++;
> - } while (level < PT64_ROOT_LEVEL-1 && !sp->unsync_children);
> -}
> -
> -static void kvm_mmu_pages_init(struct kvm_mmu_page *parent,
> - struct mmu_page_path *parents,
> - struct kvm_mmu_pages *pvec)
> -{
> - parents->parent[parent->role.level-1] = NULL;
> - pvec->nr = 0;
> + } while (!sp->unsync_children);
> }
>
> static void mmu_sync_children(struct kvm_vcpu *vcpu,
> @@ -2021,7 +2034,6 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
> struct kvm_mmu_pages pages;
> LIST_HEAD(invalid_list);
>
> - kvm_mmu_pages_init(parent, &parents, &pages);
> while (mmu_unsync_walk(parent, &pages)) {
> bool protected = false;
>
> @@ -2037,7 +2049,6 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
> }
> kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
> cond_resched_lock(&vcpu->kvm->mmu_lock);
> - kvm_mmu_pages_init(parent, &parents, &pages);
> }
> }
>
> @@ -2269,7 +2280,6 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
> if (parent->role.level == PT_PAGE_TABLE_LEVEL)
> return 0;
>
> - kvm_mmu_pages_init(parent, &parents, &pages);
> while (mmu_unsync_walk(parent, &pages)) {
> struct kvm_mmu_page *sp;
>
> @@ -2278,7 +2288,6 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
> mmu_pages_clear_parents(&parents);
> zapped++;
> }
> - kvm_mmu_pages_init(parent, &parents, &pages);
> }
>
> return zapped;
> --
> 1.8.3.1
>
>
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