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

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The commit 97e3d26b5e ("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 3f148f3318 ("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: 97e3d26b5e ("x86/mm: Randomize per-cpu entry area")
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20230306193144.24605-1-mkoutny%40suse.com
This commit is contained in:
Michal Koutný 2023-03-06 20:31:44 +01:00 committed by Dave Hansen
parent cbebd68f59
commit a3f547addc
1 changed files with 7 additions and 0 deletions
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7
arch/x86/mm/cpu_entry_area.c
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@ -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) */