[xen stable-4.16] x86/mm: add speculation barriers to open coded locks

[patchbot@xxxxxxx]

commit 41d93be76611704bdc73e8fe71c251a6f1da114c
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Mar 4 18:08:48 2024 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Mar 12 16:26:39 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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 42a572a38e22a97d86a4b648a22597628d5b42e4)
---
 xen/arch/x86/mm.c        | 6 ++++--
 xen/include/asm-x86/mm.h | 4 +++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index ea024c1450..2bf1b70985 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2005,7 +2005,7 @@ 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;
 
@@ -2066,7 +2066,7 @@ 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;
 
@@ -2075,6 +2075,8 @@ 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)
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index cccef852b4..73d5a98bec 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -393,7 +393,9 @@ 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);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16