From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FCA933F9; Sun, 24 Mar 2024 10:30:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711276251; cv=none; b=R6MmdfUDNrBfliJdkk9vlL3aPDAqAcZhfvZeTniBwpU/A44xb7zkqbbRwa+cPJXiCtyi5i+EVBTpblpxIqsawMIvjsaoPLWLvUcOwy1OVAbFe2ne0tk+DPsA3EkP+lrLOqCy8fugRUTIJt1FBqDnIwLiJuIG6Kgcz7yOzDRKdY8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711276251; c=relaxed/simple; bh=i/KBVM/hVsILZHtcXZzSHp2NdrbsYCYNR/zIoJ3kBaA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=f5BX+OK5GYKXy7ovRB6b9+08fhf3vdPOsbz8VIhlWMLNuvleO3w5/lt/FqHyBqJegcl1xe6pGui21KSdPjT3YVMSj0Ia/Hz5SJCg64I4s/JbWX56+et7/dV6/bBKYYJAbNIBa1vlUUIgHyvO0lI0rmY+QKaRwAkHHsjNfcUeebc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Y5Soixto; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y5Soixto" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 211E3C433F1; Sun, 24 Mar 2024 10:30:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711276251; bh=i/KBVM/hVsILZHtcXZzSHp2NdrbsYCYNR/zIoJ3kBaA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Y5SoixtoQOXDGlmn7h4qZyREMJ6mWoeIaoniDbaB8DYpPY4lP+Fk8FhR3xwxK1gz9 AM/JCXIvzOlhNa5wokIeF6+ZUWRYzPOvRYLye6bcgeNex82WYQCdM0mkSvmmmulpeV THXt3BFrRP2WCMTz0ZPuCrEKPSW6KRibMppHqcY663WUZURlspcm5IiTZESzoAvUKw VEMbUJukG4OZ5KnKIb4aQGbCwqGbOFfKBCaRQMeft13CXgUXLJHLDOWtKxvA52sQmr OinKzNAeqGJ5VJwisWLebE4hjcZGDXK+8ygilZGv3N0ihFBq0TVZCouP+4OQOn1IfL nOFBi5g8gWsKA== Date: Sun, 24 Mar 2024 12:29:39 +0200 From: Mike Rapoport To: David Hildenbrand Cc: Miklos Szeredi , xingwei lee , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, samsun1006219@gmail.com, syzkaller-bugs@googlegroups.com, linux-mm Subject: Re: BUG: unable to handle kernel paging request in fuse_copy_do Message-ID: References: <620f68b0-4fe0-4e3e-856a-dedb4bcdf3a7@redhat.com> <463612f2-5590-4fb3-8273-0d64c3fd3684@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Mar 22, 2024 at 10:56:08PM +0100, David Hildenbrand wrote: > On 22.03.24 22:37, David Hildenbrand wrote: > > On 22.03.24 22:33, David Hildenbrand wrote: > > > On 22.03.24 22:18, David Hildenbrand wrote: > > > > On 22.03.24 22:13, Miklos Szeredi wrote: > > > > > On Fri, 22 Mar 2024 at 22:08, David Hildenbrand wrote: > > > > > > > > > > > > On 22.03.24 20:46, Miklos Szeredi wrote: > > > > > > > On Fri, 22 Mar 2024 at 16:41, David Hildenbrand wrote: > > > > > > > > > > > > > > > But at least the vmsplice() just seems to work. Which is weird, because > > > > > > > > GUP-fast should not apply (page not faulted in?) > > > > > > > > > > > > > > But it is faulted in, and that indeed seems to be the root cause. > > > > > > > > > > > > secretmem mmap() won't populate the page tables. So it's not faulted in yet. > > > > > > > > > > > > When we GUP via vmsplice, GUP-fast should not find it in the page tables > > > > > > and fallback to slow GUP. > > > > > > > > > > > > There, we seem to pass check_vma_flags(), trigger faultin_page() to > > > > > > fault it in, and then find it via follow_page_mask(). > > > > > > > > > > > > ... and I wonder how we manage to skip check_vma_flags(), or otherwise > > > > > > managed to GUP it. > > > > > > > > > > > > vmsplice() should, in theory, never succeed here. > > > > > > > > > > > > Weird :/ > > > > > > > > > > > > > Improved repro: > > > > > > > > > > > > > > #define _GNU_SOURCE > > > > > > > > > > > > > > #include > > > > > > > #include > > > > > > > #include > > > > > > > #include > > > > > > > #include > > > > > > > #include > > > > > > > > > > > > > > int main(void) > > > > > > > { > > > > > > > int fd1, fd2; > > > > > > > int pip[2]; > > > > > > > struct iovec iov; > > > > > > > char *addr; > > > > > > > int ret; > > > > > > > > > > > > > > fd1 = syscall(__NR_memfd_secret, 0); > > > > > > > addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd1, 0); > > > > > > > ftruncate(fd1, 7); > > > > > > > addr[0] = 1; /* fault in page */ > > > > > > > > > > Here the page is faulted in and GUP-fast will find it. It's not in > > > > > the kernel page table, but it is in the user page table, which is what > > > > > matter for GUP. > > > > > > > > Trust me, I know the GUP code very well :P > > > > > > > > gup_pte_range -- GUP fast -- contains: > > > > > > > > if (unlikely(folio_is_secretmem(folio))) { > > > > gup_put_folio(folio, 1, flags); > > > > goto pte_unmap; > > > > } > > > > > > > > So we "should" be rejecting any secretmem folios and fallback to GUP slow. > > > > > > > > > > > > ... we don't check the same in gup_huge_pmd(), but we shouldn't ever see > > > > THP in secretmem code. > > > > > > > > > > Ehm: > > > > > > [ 29.441405] Secretmem fault: PFN: 1096177 > > > [ 29.442092] GUP-fast: PFN: 1096177 > > > > > > > > > ... is folio_is_secretmem() broken? > > > > > > ... is it something "obvious" like: > > > > > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > > > index 35f3a4a8ceb1e..6996f1f53f147 100644 > > > --- a/include/linux/secretmem.h > > > +++ b/include/linux/secretmem.h > > > @@ -16,7 +16,7 @@ static inline bool folio_is_secretmem(struct folio *folio) > > > * We know that secretmem pages are not compound and LRU so we can > > > * save a couple of cycles here. > > > */ > > > - if (folio_test_large(folio) || !folio_test_lru(folio)) > > > + if (folio_test_large(folio) || folio_test_lru(folio)) > > > return false; > > > mapping = (struct address_space *) > > > > ... yes, that does the trick! > > > > Proper patch (I might send out again on Monday "officially"). There are > other improvements we want to do to folio_is_secretmem() in the light of > folio_fast_pin_allowed(), that I wanted to do a while ago. I might send > a patch for that as well now that I'm at it. The most robust but a bit slower solution is to make folio_is_secretmem() call folio_mapping() rather than open code the check. What improvements did you have in mind? > From 85558a46d9f249f26bd77dd3b18d14f248464845 Mon Sep 17 00:00:00 2001 > From: David Hildenbrand > Date: Fri, 22 Mar 2024 22:45:36 +0100 > Subject: [PATCH] mm/secretmem: fix GUP-fast succeeding on secretmem folios > > folio_is_secretmem() states that secretmem folios cannot be LRU folios: > so we may only exit early if we find an LRU folio. Yet, we exit early if > we find a folio that is not a secretmem folio. > > Consequently, folio_is_secretmem() fails to detect secretmem folios and, > therefore, we can succeed in grabbing a secretmem folio during GUP-fast, > crashing the kernel when we later try reading/writing to the folio, because > the folio has been unmapped from the directmap. > > Reported-by: xingwei lee > Reported-by: yue sun > Debugged-by: Miklos Szeredi > Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas") > Cc: > Signed-off-by: David Hildenbrand Reviewed-by: Mike Rapoport (IBM) > --- > include/linux/secretmem.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > index 35f3a4a8ceb1..6996f1f53f14 100644 > --- a/include/linux/secretmem.h > +++ b/include/linux/secretmem.h > @@ -16,7 +16,7 @@ static inline bool folio_is_secretmem(struct folio *folio) > * We know that secretmem pages are not compound and LRU so we can > * save a couple of cycles here. > */ > - if (folio_test_large(folio) || !folio_test_lru(folio)) > + if (folio_test_large(folio) || folio_test_lru(folio)) > return false; > mapping = (struct address_space *) > -- > 2.43.2 > > > -- > Cheers, > > David / dhildenb > -- Sincerely yours, Mike.