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Date: Thu, 8 Apr 2021 15:56:04 +0100 From: Will Deacon <will@...nel.org> To: Vincenzo Frascino <vincenzo.frascino@....com> Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com, Catalin Marinas <catalin.marinas@....com> Subject: Re: [PATCH] arm64: mte: Move MTE TCF0 check in entry-common 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.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(); > } 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. > > 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. Will
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