* [PATCH v2 2/2] arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled
2021-09-14 21:54 [PATCH v2 1/2] arm64: add an MTE support check to the top of mte_thread_switch() Peter Collingbourne
@ 2021-09-14 21:54 ` Peter Collingbourne
2021-09-15 17:59 ` [PATCH v2 1/2] arm64: add an MTE support check to the top of mte_thread_switch() Catalin Marinas
1 sibling, 0 replies; 4+ messages in thread
From: Peter Collingbourne @ 2021-09-14 21:54 UTC (permalink / raw)
To: Catalin Marinas, Vincenzo Frascino, Will Deacon, Andrey Konovalov
Cc: Peter Collingbourne, Evgenii Stepanov, linux-arm-kernel
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
---
v2:
- add prerequisite patch to fix booting on non-MTE hardware
arch/arm64/kernel/entry.S | 10 +++++-----
arch/arm64/kernel/mte.c | 24 +++++++++++++++++++++---
include/linux/kasan.h | 9 +++++++--
3 files changed, 33 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bc6d5a970a13..2f69ae43941d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -168,9 +168,9 @@ alternative_else_nop_endif
.macro mte_set_kernel_gcr, tmp, tmp2
#ifdef CONFIG_KASAN_HW_TAGS
-alternative_if_not ARM64_MTE
+alternative_cb kasan_hw_tags_enable
b 1f
-alternative_else_nop_endif
+alternative_cb_end
mov \tmp, KERNEL_GCR_EL1
msr_s SYS_GCR_EL1, \tmp
1:
@@ -178,10 +178,10 @@ alternative_else_nop_endif
.endm
.macro mte_set_user_gcr, tsk, tmp, tmp2
-#ifdef CONFIG_ARM64_MTE
-alternative_if_not ARM64_MTE
+#ifdef CONFIG_KASAN_HW_TAGS
+alternative_cb kasan_hw_tags_enable
b 1f
-alternative_else_nop_endif
+alternative_cb_end
ldr \tmp, [\tsk, #THREAD_MTE_CTRL]
mte_set_gcr \tmp, \tmp2
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 8fc2d90eeb00..5a026a91b4bf 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -162,7 +162,7 @@ void mte_check_tfsr_el1(void)
}
#endif
-static void mte_update_sctlr_user(struct task_struct *task)
+static void mte_update_sctlr_user_and_gcr_excl(struct task_struct *task)
{
/*
* This must be called with preemption disabled and can only be called
@@ -182,6 +182,24 @@ static void mte_update_sctlr_user(struct task_struct *task)
else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC)
sctlr |= SCTLR_EL1_TCF0_SYNC;
task->thread.sctlr_user = sctlr;
+
+ /*
+ * 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())
+ write_sysreg_s(((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)
@@ -202,7 +220,7 @@ void mte_thread_switch(struct task_struct *next)
if (!system_supports_mte())
return;
- mte_update_sctlr_user(next);
+ mte_update_sctlr_user_and_gcr_excl(next);
/*
* Check if an async tag exception occurred at EL1.
@@ -247,7 +265,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
task->thread.mte_ctrl = mte_ctrl;
if (task == current) {
preempt_disable();
- mte_update_sctlr_user(task);
+ mte_update_sctlr_user_and_gcr_excl(task);
update_sctlr_el1(task->thread.sctlr_user);
preempt_enable();
}
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index dd874a1ee862..de5f5913374d 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -89,7 +89,7 @@ static __always_inline bool kasan_enabled(void)
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();
}
@@ -104,7 +104,7 @@ static inline bool kasan_enabled(void)
return IS_ENABLED(CONFIG_KASAN);
}
-static inline bool kasan_has_integrated_init(void)
+static inline bool kasan_hw_tags_enabled(void)
{
return false;
}
@@ -125,6 +125,11 @@ static __always_inline void kasan_free_pages(struct page *page,
#endif /* CONFIG_KASAN_HW_TAGS */
+static inline bool kasan_has_integrated_init(void)
+{
+ return kasan_hw_tags_enabled();
+}
+
#ifdef CONFIG_KASAN
struct kasan_cache {
--
2.33.0.309.g3052b89438-goog
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2 1/2] arm64: add an MTE support check to the top of mte_thread_switch()
2021-09-14 21:54 [PATCH v2 1/2] arm64: add an MTE support check to the top of mte_thread_switch() Peter Collingbourne
2021-09-14 21:54 ` [PATCH v2 2/2] arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled Peter Collingbourne
@ 2021-09-15 17:59 ` Catalin Marinas
2021-09-15 19:04 ` Peter Collingbourne
1 sibling, 1 reply; 4+ messages in thread
From: Catalin Marinas @ 2021-09-15 17:59 UTC (permalink / raw)
To: Peter Collingbourne
Cc: Vincenzo Frascino, Will Deacon, Andrey Konovalov,
Evgenii Stepanov, linux-arm-kernel
On Tue, Sep 14, 2021 at 02:54:28PM -0700, Peter Collingbourne wrote:
> This lets us avoid doing unnecessary work on hardware that does
> not support MTE, and will allow us to freely use MTE instructions
> in the code called by mte_thread_switch().
>
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Link: https://linux-review.googlesource.com/id/I02fd000d1ef2c86c7d2952a7f099b254ec227a5d
> ---
> arch/arm64/kernel/mte.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index 9d314a3bad3b..8fc2d90eeb00 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -199,6 +199,9 @@ void mte_thread_init_user(void)
>
> void mte_thread_switch(struct task_struct *next)
> {
> + if (!system_supports_mte())
> + return;
> +
> mte_update_sctlr_user(next);
Ah, good point. While you are at this, could you please remove the
system_supports_mte() check from mte_check_tfsr_el1() and add it to
mte_check_tfsr_entry/exit? On the exit path, we unnecessarily do a
dsb+isb even when MTE is not present.
I guess we could also skip the tfsr_el1 check if
!system_uses_mte_async_mode() (well, I'd need to page in which TFSR bits
are set for uaccess).
Thanks.
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread