Mailing List Archive

commit 42a572a38e22a97d86a4b648a22597628d5b42e4
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Mon Mar 4 18:08:48 2024 +0100
Commit: Andrew Cooper <andrew.cooper3@citrix.com>
CommitDate: Tue Mar 12 15:50:04 2024 +0000

x86/mm: add speculation barriers to open coded locks

Add a speculation barrier to the clearly identified open-coded lock taking
functions.

Note that the memory sharing page_lock() replacement (_page_lock()) is left
as-is, as the code is experimental and not security supported.

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>
---
xen/arch/x86/include/asm/mm.h | 4 +++-
xen/arch/x86/mm.c | 6 ++++--
2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
index 7d26d9cd2f..65d209d5ff 100644
--- a/xen/arch/x86/include/asm/mm.h
+++ b/xen/arch/x86/include/asm/mm.h
@@ -399,7 +399,9 @@ const struct platform_bad_page *get_platform_badpages(unsigned int *array_size);
* The use of PGT_locked in mem_sharing does not collide, since mem_sharing is
* only supported for hvm guests, which do not have PV PTEs updated.
*/
-int page_lock(struct page_info *page);
+int page_lock_unsafe(struct page_info *page);
+#define page_lock(pg) lock_evaluate_nospec(page_lock_unsafe(pg))
+
void page_unlock(struct page_info *page);

void put_page_type(struct page_info *page);
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 0c6658298d..2ba4c26401 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2034,7 +2034,7 @@ static inline bool current_locked_page_ne_check(struct page_info *page) {
#define current_locked_page_ne_check(x) true
#endif

-int page_lock(struct page_info *page)
+int page_lock_unsafe(struct page_info *page)
{
unsigned long x, nx;

@@ -2095,7 +2095,7 @@ void page_unlock(struct page_info *page)
* l3t_lock(), so to avoid deadlock we must avoid grabbing them in
* reverse order.
*/
-static void l3t_lock(struct page_info *page)
+static always_inline void l3t_lock(struct page_info *page)
{
unsigned long x, nx;

@@ -2104,6 +2104,8 @@ static void l3t_lock(struct page_info *page)
cpu_relax();
nx = x | PGT_locked;
} while ( cmpxchg(&page->u.inuse.type_info, x, nx) != x );
+
+ block_lock_speculation();
}

static void l3t_unlock(struct page_info *page)
--
generated by git-patchbot for /home/xen/git/xen.git#master