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To: Sebastian Andrzej Siewior , Sami Tolvanen Cc: linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Gomez , Luis Chamberlain , "Paul E . McKenney" , Peter Zijlstra , Thomas Gleixner , Elliot Berman , Kees Cook , Nathan Chancellor , Steven Rostedt , llvm@lists.linux.dev References: <20241220174731.514432-1-bigeasy@linutronix.de> <20241220174731.514432-29-bigeasy@linutronix.de> Content-Language: en-US From: Petr Pavlu In-Reply-To: <20241220174731.514432-29-bigeasy@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/20/24 18:41, Sebastian Andrzej Siewior wrote: > __module_address() can be invoked within a RCU section, there is no > requirement to have preemption disabled. > > I'm not sure if using rcu_read_lock() will introduce the regression that > has been fixed in commit 14c4c8e41511a ("cfi: Use > rcu_read_{un}lock_sched_notrace"). > > Cc: Elliot Berman > Cc: Kees Cook > Cc: Nathan Chancellor > Cc: Sami Tolvanen > Cc: Steven Rostedt > Cc: llvm@lists.linux.dev > Signed-off-by: Sebastian Andrzej Siewior > --- > kernel/cfi.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/cfi.c b/kernel/cfi.c > index 08caad7767176..c8f2b5a51b2e6 100644 > --- a/kernel/cfi.c > +++ b/kernel/cfi.c > @@ -71,6 +71,10 @@ static bool is_module_cfi_trap(unsigned long addr) > struct module *mod; > bool found = false; > > + /* > + * XXX this could be RCU protected but would it introcude the regression > + * fixed in 14c4c8e41511a ("cfi: Use rcu_read_{un}lock_sched_notrace") > + */ > rcu_read_lock_sched_notrace(); > > mod = __module_address(addr); I think that since 89245600941e ("cfi: Switch to -fsanitize=kcfi"), this can be a call to rcu_read_lock_sched(), or in your case rcu_read_lock(). The recursive case where __cfi_slowpath_diag() could end up calling itself is no longer present, as all that logic is gone. I then don't see another reason this should use the notrace variant. @Sami, could you please confirm this? -- Thanks, Petr