From: Michal Koutný <mkoutny@xxxxxxxx>
commit a3f547addcaa10df5a226526bc9e2d9a94542344 upstream.
The commit 97e3d26b5e5f ("x86/mm: Randomize per-cpu entry area") fixed
an omission of KASLR on CPU entry areas. It doesn't take into account
KASLR switches though, which may result in unintended non-determinism
when a user wants to avoid it (e.g. debugging, benchmarking).
Generate only a single combination of CPU entry areas offsets -- the
linear array that existed prior randomization when KASLR is turned off.
Since we have 3f148f331814 ("x86/kasan: Map shadow for percpu pages on
demand") and followups, we can use the more relaxed guard
kasrl_enabled() (in contrast to kaslr_memory_enabled()).
Fixes: 97e3d26b5e5f ("x86/mm: Randomize per-cpu entry area")
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20230306193144.24605-1-mkoutny%40suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/cpu_entry_area.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 7316a8224259..e91500a80963 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -10,6 +10,7 @@
#include <asm/fixmap.h>
#include <asm/desc.h>
#include <asm/kasan.h>
+#include <asm/setup.h>
static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);
@@ -29,6 +30,12 @@ static __init void init_cea_offsets(void)
unsigned int max_cea;
unsigned int i, j;
+ if (!kaslr_enabled()) {
+ for_each_possible_cpu(i)
+ per_cpu(_cea_offset, i) = i;
+ return;
+ }
+
max_cea = (CPU_ENTRY_AREA_MAP_SIZE - PAGE_SIZE) / CPU_ENTRY_AREA_SIZE;
/* O(sodding terrible) */
--
2.40.0
