Messages in this thread Patch in this message | | | From | Michal Koutný <> | Subject | [PATCH v2] x86/mm: Do not shuffle CPU entry areas without KASLR | Date | Mon, 6 Mar 2023 20:31:44 +0100 |
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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@suse.com> ---
v1: https://lore.kernel.org/r/20230303160645.3594-1-mkoutny@suse.com
Changes in v2: - s/kaslr_memory_enabled/kasrl_enabled/, commit message
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) */ -- 2.39.2
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