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Thu, 22 Oct 2026 12:39:20 -0700 (PDT) Received: from krava ([176.74.159.170]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a2101cedcesm20827015e9.0.2026.10.22.12.39.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 12:39:19 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 22 Oct 2026 21:39:18 +0200 To: "Lorenzo Stoakes (ARM)" Cc: Alexei Starovoitov , Daniel Borkmann , bpf@vger.kernel.org, Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , linux-mm@kvack.org, Andrew Morton , "Liam R. Howlett" , linux-kselftest@vger.kernel.org, Shuah Khan , John Fastabend Subject: Re: [RFC bpf-next 3/9] mm: Expose locked mprotect operation Message-ID: References: <20261021195759.119421-1-jolsa@kernel.org> <20261021195759.119421-4-jolsa@kernel.org> X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Oct 22, 2026 at 11:25:31AM +0100, Lorenzo Stoakes (ARM) wrote: > On Wed, Oct 21, 2026 at 09:57:52PM +0200, Jiri Olsa wrote: > > The bpf_user_page_exec() in following patch needs to change page > > protections while holding current->mm's mmap write lock. > > > > Exposing the do_mprotect_pkey_locked helper for that. > > Err, we'll need some more justification than this for exposing internal mm > logic to the rest of the kernel please. > > Note that you're already allowing any caller to bypass > CONFIG_ARCH_HAS_PKEYS here which is immediately a broken thing. > > > > > Assisted-by: Codex:GPT-6 > > Signed-off-by: Jiri Olsa > > It's a no to this in its current form. yes I suspected it'd be a problem, but as you mentioned in the other reply, Alexei's proposal takes care of that thanks, jirka > > > --- > > include/linux/mm.h | 3 +++ > > mm/mprotect.c | 20 +++++++++++++++----- > > 2 files changed, 18 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 63f40e615754..47e853093601 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -3435,6 +3435,9 @@ extern long change_protection(struct mmu_gather *tlb, > > extern int mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb, > > struct vm_area_struct *vma, struct vm_area_struct **pprev, > > unsigned long start, unsigned long end, vm_flags_t newflags); > > +/* Caller must hold current->mm's mmap write lock. */ > > +int do_mprotect_pkey_locked(unsigned long start, size_t len, > > + unsigned long prot, int pkey); > > > > /* > > * doesn't attempt to fault and will return short. > > diff --git a/mm/mprotect.c b/mm/mprotect.c > > index 2888ee638d87..8d800830d3e1 100644 > > --- a/mm/mprotect.c > > +++ b/mm/mprotect.c > > @@ -868,8 +868,8 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb, > > /* > > * pkey==-1 when doing a legacy mprotect() > > */ > > -static int do_mprotect_pkey(unsigned long start, size_t len, > > - unsigned long prot, int pkey) > > +int do_mprotect_pkey_locked(unsigned long start, size_t len, > > + unsigned long prot, int pkey) > > { > > unsigned long nstart, end, tmp, reqprot; > > struct vm_area_struct *vma, *prev; > > @@ -899,8 +899,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len, > > > > reqprot = prot; > > > > - if (mmap_write_lock_killable(current->mm)) > > - return -EINTR; > > + mmap_assert_write_locked(current->mm); > > > > /* > > * If userspace did not allocate the pkey, do not let > > @@ -1013,10 +1012,21 @@ static int do_mprotect_pkey(unsigned long start, size_t len, > > error = -ENOMEM; > > > > out: > > - mmap_write_unlock(current->mm); > > return error; > > } > > > > +static int do_mprotect_pkey(unsigned long start, size_t len, > > + unsigned long prot, int pkey) > > +{ > > + int ret; > > + > > + if (mmap_write_lock_killable(current->mm)) > > + return -EINTR; > > + ret = do_mprotect_pkey_locked(start, len, prot, pkey); > > + mmap_write_unlock(current->mm); > > + return ret; > > +} > > + > > SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len, > > unsigned long, prot) > > { > > -- > > 2.54.0 > > > > -- > Cheers, Lorenzo