Commit a3f547ad authored by Michal Koutný's avatar Michal Koutný Committed by Dave Hansen
Browse files

x86/mm: Do not shuffle CPU entry areas without KASLR 



The commit 97e3d26b ("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 3f148f33 ("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: 97e3d26b ("x86/mm: Randomize per-cpu entry area")
Signed-off-by: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20230306193144.24605-1-mkoutny%40suse.com
parent cbebd68f

arch/x86/mm/cpu_entry_area.c

+7 −0
Original line number Diff line number Diff line
@@ -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) */