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arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled 

It is not necessary to write to GCR_EL1 on every kernel entry and
exit when HW tag-based KASAN is disabled because the kernel will not
execute any IRG instructions in that mode. Since accessing GCR_EL1
can be expensive on some microarchitectures, avoid doing so by moving
the access to task switch when HW tag-based KASAN is disabled.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://linux-review.googlesource.com/id/I78e90d60612a94c24344526f476ac4ff216e10d2
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210924010655.2886918-1-pcc@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Peter Collingbourne 2021-09-23 18:06:55 -07:00 committed by Will Deacon
parent 5816b3e657
commit e5af50a5df
3 changed files with 38 additions and 7 deletions
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10
arch/arm64/kernel/entry.S
View File

@ -168,9 +168,9 @@ alternative_else_nop_endif
.macro mte_set_kernel_gcr, tmp, tmp2 .macro mte_set_kernel_gcr, tmp, tmp2
#ifdef CONFIG_KASAN_HW_TAGS #ifdef CONFIG_KASAN_HW_TAGS
alternative_if_not ARM64_MTE alternative_cb kasan_hw_tags_enable
b 1f b 1f
alternative_else_nop_endif alternative_cb_end
mov \tmp, KERNEL_GCR_EL1 mov \tmp, KERNEL_GCR_EL1
msr_s SYS_GCR_EL1, \tmp msr_s SYS_GCR_EL1, \tmp
1: 1:
@ -178,10 +178,10 @@ alternative_else_nop_endif
.endm .endm
.macro mte_set_user_gcr, tsk, tmp, tmp2 .macro mte_set_user_gcr, tsk, tmp, tmp2
#ifdef CONFIG_ARM64_MTE #ifdef CONFIG_KASAN_HW_TAGS
alternative_if_not ARM64_MTE alternative_cb kasan_hw_tags_enable
b 1f b 1f
alternative_else_nop_endif alternative_cb_end
ldr \tmp, [\tsk, #THREAD_MTE_CTRL] ldr \tmp, [\tsk, #THREAD_MTE_CTRL]
mte_set_gcr \tmp, \tmp2 mte_set_gcr \tmp, \tmp2

26
arch/arm64/kernel/mte.c
View File

@ -179,6 +179,30 @@ static void mte_update_sctlr_user(struct task_struct *task)
task->thread.sctlr_user = sctlr; task->thread.sctlr_user = sctlr;
} }
static void mte_update_gcr_excl(struct task_struct *task)
{
/*
* SYS_GCR_EL1 will be set to current->thread.mte_ctrl value by
* mte_set_user_gcr() in kernel_exit, but only if KASAN is enabled.
*/
if (kasan_hw_tags_enabled())
return;
write_sysreg_s(
((task->thread.mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) &
SYS_GCR_EL1_EXCL_MASK) | SYS_GCR_EL1_RRND,
SYS_GCR_EL1);
}
void __init kasan_hw_tags_enable(struct alt_instr *alt, __le32 *origptr,
__le32 *updptr, int nr_inst)
{
BUG_ON(nr_inst != 1); /* Branch -> NOP */
if (kasan_hw_tags_enabled())
*updptr = cpu_to_le32(aarch64_insn_gen_nop());
}
void mte_thread_init_user(void) void mte_thread_init_user(void)
{ {
if (!system_supports_mte()) if (!system_supports_mte())
@ -198,6 +222,7 @@ void mte_thread_switch(struct task_struct *next)
return; return;
mte_update_sctlr_user(next); mte_update_sctlr_user(next);
mte_update_gcr_excl(next);
/* /*
* Check if an async tag exception occurred at EL1. * Check if an async tag exception occurred at EL1.
@ -243,6 +268,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
if (task == current) { if (task == current) {
preempt_disable(); preempt_disable();
mte_update_sctlr_user(task); mte_update_sctlr_user(task);
mte_update_gcr_excl(task);
update_sctlr_el1(task->thread.sctlr_user); update_sctlr_el1(task->thread.sctlr_user);
preempt_enable(); preempt_enable();
} }

9
include/linux/kasan.h
View File

@ -89,7 +89,7 @@ static __always_inline bool kasan_enabled(void)
return static_branch_likely(&kasan_flag_enabled); return static_branch_likely(&kasan_flag_enabled);
} }
static inline bool kasan_has_integrated_init(void) static inline bool kasan_hw_tags_enabled(void)
{ {
return kasan_enabled(); return kasan_enabled();
} }
@ -104,7 +104,7 @@ static inline bool kasan_enabled(void)
return IS_ENABLED(CONFIG_KASAN); return IS_ENABLED(CONFIG_KASAN);
} }
static inline bool kasan_has_integrated_init(void) static inline bool kasan_hw_tags_enabled(void)
{ {
return false; return false;
} }
@ -125,6 +125,11 @@ static __always_inline void kasan_free_pages(struct page *page,
#endif /* CONFIG_KASAN_HW_TAGS */ #endif /* CONFIG_KASAN_HW_TAGS */
static inline bool kasan_has_integrated_init(void)
{
return kasan_hw_tags_enabled();
}
#ifdef CONFIG_KASAN #ifdef CONFIG_KASAN
struct kasan_cache { struct kasan_cache {