Mailing List Archive

commit 0fb100a94d0127910fe1dfa253cb759f6bc11174
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Mon Mar 4 16:24:21 2024 +0100
Commit: Andrew Cooper <andrew.cooper3@citrix.com>
CommitDate: Tue Mar 12 16:37:45 2024 +0000

x86: protect conditional lock taking from speculative execution

Conditionally taken locks that use the pattern:

if ( lock )
spin_lock(...);

Need an else branch in order to issue an speculation barrier in the else case,
just like it's done in case the lock needs to be acquired.

eval_nospec() could be used on the condition itself, but that would result in a
double barrier on the branch where the lock is taken.

Introduce a new pair of helpers, {gfn,spin}_lock_if() that can be used to
conditionally take a lock in a speculation safe way.

This is part of XSA-453 / CVE-2024-2193

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 03cf7ca23e0e876075954c558485b267b7d02406)
---
xen/arch/x86/mm.c | 37 +++++++++++++++----------------------
xen/arch/x86/mm/mm-locks.h | 9 +++++++++
xen/arch/x86/mm/p2m.c | 5 ++---
xen/include/xen/spinlock.h | 8 ++++++++
4 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index ad22543d1b..ffee1c6bd1 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4978,8 +4978,7 @@ static l3_pgentry_t *virt_to_xen_l3e(unsigned long v)
if ( !l3t )
return NULL;
clear_page(l3t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l4e_get_flags(*pl4e) & _PAGE_PRESENT) )
{
l4_pgentry_t l4e = l4e_from_paddr(__pa(l3t), __PAGE_HYPERVISOR);
@@ -5013,8 +5012,7 @@ static l2_pgentry_t *virt_to_xen_l2e(unsigned long v)
if ( !l2t )
return NULL;
clear_page(l2t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l3e_get_flags(*pl3e) & _PAGE_PRESENT) )
{
l3e_write(pl3e, l3e_from_paddr(__pa(l2t), __PAGE_HYPERVISOR));
@@ -5046,8 +5044,7 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
if ( !l1t )
return NULL;
clear_page(l1t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) )
{
l2e_write(pl2e, l2e_from_paddr(__pa(l1t), __PAGE_HYPERVISOR));
@@ -5076,6 +5073,8 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
do { \
if ( locking ) \
l3t_lock(page); \
+ else \
+ block_lock_speculation(); \
} while ( false )

#define L3T_UNLOCK(page) \
@@ -5284,8 +5283,7 @@ int map_pages_to_xen(
if ( l3e_get_flags(ol3e) & _PAGE_GLOBAL )
flush_flags |= FLUSH_TLB_GLOBAL;

- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
(l3e_get_flags(*pl3e) & _PAGE_PSE) )
{
@@ -5384,8 +5382,7 @@ int map_pages_to_xen(
if ( l2e_get_flags(*pl2e) & _PAGE_GLOBAL )
flush_flags |= FLUSH_TLB_GLOBAL;

- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
(l2e_get_flags(*pl2e) & _PAGE_PSE) )
{
@@ -5424,8 +5421,7 @@ int map_pages_to_xen(
unsigned long base_mfn;
const l1_pgentry_t *l1t;

- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);

ol2e = *pl2e;
/*
@@ -5478,8 +5474,7 @@ int map_pages_to_xen(
unsigned long base_mfn;
const l2_pgentry_t *l2t;

- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);

ol3e = *pl3e;
/*
@@ -5614,8 +5609,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
l2e_from_pfn(l3e_get_pfn(*pl3e) +
(i << PAGETABLE_ORDER),
l3e_get_flags(*pl3e)));
- if ( locking )
- spin_lock(&map_pgdir_lock);
+
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
(l3e_get_flags(*pl3e) & _PAGE_PSE) )
{
@@ -5671,8 +5666,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
l1e_write(&l1t[i],
l1e_from_pfn(l2e_get_pfn(*pl2e) + i,
l2e_get_flags(*pl2e) & ~_PAGE_PSE));
- if ( locking )
- spin_lock(&map_pgdir_lock);
+
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
(l2e_get_flags(*pl2e) & _PAGE_PSE) )
{
@@ -5714,8 +5709,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
*/
if ( (nf & _PAGE_PRESENT) || ((v != e) && (l1_table_offset(v) != 0)) )
continue;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);

/*
* L2E may be already cleared, or set to a superpage, by
@@ -5760,8 +5754,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
if ( (nf & _PAGE_PRESENT) ||
((v != e) && (l2_table_offset(v) + l1_table_offset(v) != 0)) )
continue;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);

/*
* L3E may be already cleared, or set to a superpage, by
diff --git a/xen/arch/x86/mm/mm-locks.h b/xen/arch/x86/mm/mm-locks.h
index cc635a4405..7eee233b4c 100644
--- a/xen/arch/x86/mm/mm-locks.h
+++ b/xen/arch/x86/mm/mm-locks.h
@@ -347,6 +347,15 @@ static inline void p2m_unlock(struct p2m_domain *p)
#define p2m_locked_by_me(p) mm_write_locked_by_me(&(p)->lock)
#define gfn_locked_by_me(p,g) p2m_locked_by_me(p)

+static always_inline void gfn_lock_if(bool condition, struct p2m_domain *p2m,
+ gfn_t gfn, unsigned int order)
+{
+ if ( condition )
+ gfn_lock(p2m, gfn, order);
+ else
+ block_lock_speculation();
+}
+
/* PoD lock (per-p2m-table)
*
* Protects private PoD data structs: entry and cache
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 107f6778a6..596928e083 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -509,9 +509,8 @@ mfn_t __get_gfn_type_access(struct p2m_domain *p2m, unsigned long gfn_l,
return _mfn(gfn_l);
}

- if ( locked )
- /* Grab the lock here, don't release until put_gfn */
- gfn_lock(p2m, gfn, 0);
+ /* Grab the lock here, don't release until put_gfn */
+ gfn_lock_if(locked, p2m, gfn, 0);

mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL);

diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index efdb21ea90..8bffb3f4b6 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -216,6 +216,14 @@ static always_inline void spin_lock_irq(spinlock_t *l)
block_lock_speculation(); \
})

+/* Conditionally take a spinlock in a speculation safe way. */
+static always_inline void spin_lock_if(bool condition, spinlock_t *l)
+{
+ if ( condition )
+ _spin_lock(l);
+ block_lock_speculation();
+}
+
#define spin_unlock(l) _spin_unlock(l)
#define spin_unlock_irq(l) _spin_unlock_irq(l)
#define spin_unlock_irqrestore(l, f) _spin_unlock_irqrestore(l, f)
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.15