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Message-Id: <20210408143723.13024-1-vincenzo.frascino@arm.com>
Date: Thu, 8 Apr 2021 15:37:23 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
kasan-dev@...glegroups.com
Cc: Vincenzo Frascino <vincenzo.frascino@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Subject: [PATCH] arm64: mte: Move MTE TCF0 check in entry-common
The check_mte_async_tcf macro sets the TIF flag non-atomically. This can
race with another CPU doing a set_tsk_thread_flag() and the flag can be
lost in the process.
Move the tcf0 check to enter_from_user_mode() and clear tcf0 in
exit_to_user_mode() to address the problem.
Note: Moving the check in entry-common allows to use set_thread_flag()
which is safe.
Fixes: 637ec831ea4f ("arm64: mte: Handle synchronous and asynchronous
tag check faults")
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Reported-by: Will Deacon <will@...nel.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
---
arch/arm64/include/asm/mte.h | 8 ++++++++
arch/arm64/kernel/entry-common.c | 6 ++++++
arch/arm64/kernel/entry.S | 30 ------------------------------
arch/arm64/kernel/mte.c | 25 +++++++++++++++++++++++--
4 files changed, 37 insertions(+), 32 deletions(-)
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 9b557a457f24..188f778c6f7b 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -31,6 +31,8 @@ void mte_invalidate_tags(int type, pgoff_t offset);
void mte_invalidate_tags_area(int type);
void *mte_allocate_tag_storage(void);
void mte_free_tag_storage(char *storage);
+void check_mte_async_tcf0(void);
+void clear_mte_async_tcf0(void);
#ifdef CONFIG_ARM64_MTE
@@ -83,6 +85,12 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child,
{
return -EIO;
}
+void check_mte_async_tcf0(void)
+{
+}
+void clear_mte_async_tcf0(void)
+{
+}
static inline void mte_assign_mem_tag_range(void *addr, size_t size)
{
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 9d3588450473..837d3624a1d5 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -289,10 +289,16 @@ asmlinkage void noinstr enter_from_user_mode(void)
CT_WARN_ON(ct_state() != CONTEXT_USER);
user_exit_irqoff();
trace_hardirqs_off_finish();
+
+ /* Check for asynchronous tag check faults in user space */
+ check_mte_async_tcf0();
}
asmlinkage void noinstr exit_to_user_mode(void)
{
+ /* Ignore asynchronous tag check faults in the uaccess routines */
+ clear_mte_async_tcf0();
+
trace_hardirqs_on_prepare();
lockdep_hardirqs_on_prepare(CALLER_ADDR0);
user_enter_irqoff();
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index a31a0a713c85..fafd74ae5021 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -147,32 +147,6 @@ alternative_cb_end
.L__asm_ssbd_skip\@:
.endm
- /* Check for MTE asynchronous tag check faults */
- .macro check_mte_async_tcf, flgs, tmp
-#ifdef CONFIG_ARM64_MTE
-alternative_if_not ARM64_MTE
- b 1f
-alternative_else_nop_endif
- mrs_s \tmp, SYS_TFSRE0_EL1
- tbz \tmp, #SYS_TFSR_EL1_TF0_SHIFT, 1f
- /* Asynchronous TCF occurred for TTBR0 access, set the TI flag */
- orr \flgs, \flgs, #_TIF_MTE_ASYNC_FAULT
- str \flgs, [tsk, #TSK_TI_FLAGS]
- msr_s SYS_TFSRE0_EL1, xzr
-1:
-#endif
- .endm
-
- /* Clear the MTE asynchronous tag check faults */
- .macro clear_mte_async_tcf
-#ifdef CONFIG_ARM64_MTE
-alternative_if ARM64_MTE
- dsb ish
- msr_s SYS_TFSRE0_EL1, xzr
-alternative_else_nop_endif
-#endif
- .endm
-
.macro mte_set_gcr, tmp, tmp2
#ifdef CONFIG_ARM64_MTE
/*
@@ -243,8 +217,6 @@ alternative_else_nop_endif
ldr x19, [tsk, #TSK_TI_FLAGS]
disable_step_tsk x19, x20
- /* Check for asynchronous tag check faults in user space */
- check_mte_async_tcf x19, x22
apply_ssbd 1, x22, x23
ptrauth_keys_install_kernel tsk, x20, x22, x23
@@ -775,8 +747,6 @@ SYM_CODE_START_LOCAL(ret_to_user)
cbnz x2, work_pending
finish_ret_to_user:
user_enter_irqoff
- /* Ignore asynchronous tag check faults in the uaccess routines */
- clear_mte_async_tcf
enable_step_tsk x19, x2
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
bl stackleak_erase
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index b3c70a612c7a..e759b0eca47e 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -166,14 +166,35 @@ static void set_gcr_el1_excl(u64 excl)
*/
}
+void check_mte_async_tcf0(void)
+{
+ /*
+ * dsb(ish) is not required before the register read
+ * because the TFSRE0_EL1 is automatically synchronized
+ * by the hardware on exception entry as SCTLR_EL1.ITFSB
+ * is set.
+ */
+ u64 tcf0 = read_sysreg_s(SYS_TFSRE0_EL1);
+
+ if (tcf0 & SYS_TFSR_EL1_TF0)
+ set_thread_flag(TIF_MTE_ASYNC_FAULT);
+
+ write_sysreg_s(0, SYS_TFSRE0_EL1);
+}
+
+void clear_mte_async_tcf0(void)
+{
+ dsb(ish);
+ write_sysreg_s(0, SYS_TFSRE0_EL1);
+}
+
void flush_mte_state(void)
{
if (!system_supports_mte())
return;
/* clear any pending asynchronous tag fault */
- dsb(ish);
- write_sysreg_s(0, SYS_TFSRE0_EL1);
+ clear_mte_async_tcf0();
clear_thread_flag(TIF_MTE_ASYNC_FAULT);
/* disable tag checking */
set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
--
2.30.2
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