On Thu, Apr 08, 2021 at 03:56:04PM +0100, Will Deacon wrote: > On Thu, Apr 08, 2021 at 03:37:23PM +0100, Vincenzo Frascino wrote: > > 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. > > Actually, it's all the *other* flags that get lost! > > > 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.mari...@arm.com> > > Cc: Will Deacon <w...@kernel.org> > > Reported-by: Will Deacon <w...@kernel.org> > > Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.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(); > > } > > Is enter_from_user_mode() always called when we enter the kernel from EL0? > afaict, some paths (e.g. el0_irq()) only end up calling it if > CONTEXT_TRACKING or TRACE_IRQFLAGS are enabled.
Currently everything that's in {enter,exit}_from_user_mode() only matters when either CONTEXT_TRACKING or TRACE_IRQFLAGS is selected (and expands to an empty stub otherwise). We could drop the ifdeffery in user_{enter,exit}_irqoff() to have them called regardless, or add CONFIG_MTE to the list. > > asmlinkage void noinstr exit_to_user_mode(void) > > { > > + /* Ignore asynchronous tag check faults in the uaccess routines */ > > + clear_mte_async_tcf0(); > > + > > and this one seems to be called even less often. This is always done in ret_to_user, so (modulo ifdeferry above) all returns to EL0 call this. Thanks, Mark.