x86/shadow: account for log-dirty mode when pre-allocating

Pre-allocation is intended to ensure that in the course of constructing
or updating shadows there won't be any risk of just made shadows or
shadows being acted upon can disappear under our feet. The amount of
pages pre-allocated then, however, needs to account for all possible
subsequent allocations. While the use in sh_page_fault() accounts for
all shadows which may need making, so far it didn't account for
allocations coming from log-dirty tracking (which piggybacks onto the
P2M allocation functions).

Since shadow_prealloc() takes a count of shadows (or other data
structures) rather than a count of pages, putting the adjustment at the
call site of this function won't work very well: We simply can't express
the correct count that way in all cases. Instead take care of this in
the function itself, by "snooping" for L1 type requests. (While not
applicable right now, future new request sites of L1 tables would then
also be covered right away.)

It is relevant to note here that pre-allocations like the one done from
shadow_alloc_p2m_page() are benign when they fall in the "scope" of an
earlier pre-alloc which already included that count: The inner call will
simply find enough pages available then; it'll bail right away.

This is CVE-2022-42332 / XSA-427.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
(cherry picked from commit 91767a71061035ae42be93de495cd976f863a41a)

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 579d01c1613bc68b93e79121ff0788f287507ecd..ab1cdf1e7278429ae336eb8d1e934bf9d5019c2a 100644 (file)
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -280,6 +280,7 @@ void paging_mark_pfn_dirty(struct domain *d, pfn_t pfn)
     if ( unlikely(!VALID_M2P(pfn_x(pfn))) )
         return;
 
+    BUILD_BUG_ON(paging_logdirty_levels() != 4);
     i1 = L1_LOGDIRTY_IDX(pfn);
     i2 = L2_LOGDIRTY_IDX(pfn);
     i3 = L3_LOGDIRTY_IDX(pfn);

diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index e36d49d1fcba080813a2e7b01cbf0fc6da204e8b..e73931573b8d9669ef4bd6c9ac0e4ac4b6ead8d4 100644 (file)
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -1014,7 +1014,17 @@ bool shadow_prealloc(struct domain *d, unsigned int type, unsigned int count)
     if ( unlikely(d->is_dying) )
        return false;
 
-    ret = _shadow_prealloc(d, shadow_size(type) * count);
+    count *= shadow_size(type);
+    /*
+     * Log-dirty handling may result in allocations when populating its
+     * tracking structures.  Tie this to the caller requesting space for L1
+     * shadows.
+     */
+    if ( paging_mode_log_dirty(d) &&
+         ((SHF_L1_ANY | SHF_FL1_ANY) & (1u << type)) )
+        count += paging_logdirty_levels();
+
+    ret = _shadow_prealloc(d, count);
     if ( !ret && (!d->is_shutting_down || d->shutdown_code != SHUTDOWN_crash) )
         /*
          * Failing to allocate memory required for shadow usage can only result in

diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h
index 3fe0388e7c4f84b182c9b1ef16a8264acac1b9f3..1be84fc9518dd42d4f89fb723939244b7159d4e5 100644 (file)
--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -269,6 +269,7 @@ static inline void sh_terminate_list(struct page_list_head *tmp_list)
 #define SHF_64  (SHF_L1_64|SHF_FL1_64|SHF_L2_64|SHF_L2H_64|SHF_L3_64|SHF_L4_64)
 
 #define SHF_L1_ANY  (SHF_L1_32|SHF_L1_PAE|SHF_L1_64)
+#define SHF_FL1_ANY (SHF_FL1_32|SHF_FL1_PAE|SHF_FL1_64)
 
 #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC)
 /* Marks a guest L1 page table which is shadowed but not write-protected.

diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index eb2365297851a3744e9c8aea2158392419e7cd5b..5ec508a3514101e61f9956173a3ab1a6a10be1e0 100644 (file)
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -190,6 +190,10 @@ int paging_mfn_is_dirty(struct domain *d, mfn_t gmfn);
 #define L4_LOGDIRTY_IDX(pfn) ((pfn_x(pfn) >> (PAGE_SHIFT + 3 + PAGETABLE_ORDER * 2)) & \
                               (LOGDIRTY_NODE_ENTRIES-1))
 
+#define paging_logdirty_levels() \
+    (DIV_ROUND_UP(PADDR_BITS - PAGE_SHIFT - (PAGE_SHIFT + 3), \
+                  PAGE_SHIFT - ilog2(sizeof(mfn_t))) + 1)
+
 #ifdef CONFIG_HVM
 /* VRAM dirty tracking support */
 struct sh_dirty_vram {