On Wed, Mar 01, 2023 at 12:17:29PM +0100, Jakob Koschel wrote: > If &encl_mm->encl->mm_list does not contain the searched 'encl_mm', > 'tmp' will not point to a valid sgx_encl_mm struct. > > Linus proposed to avoid any use of the list iterator variable after the > loop, in the attempt to move the list iterator variable declaration into > the marcro to avoid any potential misuse after the loop. > Using it in a pointer comparision after the loop is undefined behavior > and should be omitted if possible [1]. > > Instead we'll just use a 'found' boolean to indicate if an element > was found. > > Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@xxxxxxxxxxxxxx/ [1] > Signed-off-by: Jakob Koschel <jkl820.git@xxxxxxxxx> > --- > Changes in v2: > - refactor to use 'found' variable instead of moving code into the loop > - add cover letter info into the patch > - Link to v1: https://lore.kernel.org/r/20230206-sgx-use-after-iter-v1-1-c09fb5300b5e@xxxxxxxxx > --- > arch/x86/kernel/cpu/sgx/encl.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c > index 2a0e90fe2abc..91fa70e51004 100644 > --- a/arch/x86/kernel/cpu/sgx/encl.c > +++ b/arch/x86/kernel/cpu/sgx/encl.c > @@ -755,6 +755,7 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn, > { > struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm, mmu_notifier); > struct sgx_encl_mm *tmp = NULL; > + bool found = false; > > /* > * The enclave itself can remove encl_mm. Note, objects can't be moved > @@ -764,12 +765,13 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn, > list_for_each_entry(tmp, &encl_mm->encl->mm_list, list) { > if (tmp == encl_mm) { > list_del_rcu(&encl_mm->list); > + found = true; > break; > } > } > spin_unlock(&encl_mm->encl->mm_lock); > > - if (tmp == encl_mm) { > + if (found) { > synchronize_srcu(&encl_mm->encl->srcu); > mmu_notifier_put(mn); > } > > --- > base-commit: d2d11f342b179f1894a901f143ec7c008caba43e > change-id: 20230206-sgx-use-after-iter-f584c1d64c87 > > Best regards, > -- > Jakob Koschel <jkl820.git@xxxxxxxxx> > Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> BR, Jarkko
