linux-kernel - Re: [PATCH v19 04/15] mm: untag user pointers passed to memory syscalls

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Message-ID: <20190809160301.GB23083@arrakis.emea.arm.com>
Date:   Fri, 9 Aug 2019 17:03:01 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-media@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v19 04/15] mm: untag user pointers passed to memory
 syscalls

On Tue, Jul 23, 2019 at 07:58:41PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends kernel ABI to allow to pass
> tagged user pointers (with the top byte set to something else other than
> 0x00) as syscall arguments.
> 
> This patch allows tagged pointers to be passed to the following memory
> syscalls: get_mempolicy, madvise, mbind, mincore, mlock, mlock2, mprotect,
> mremap, msync, munlock, move_pages.
> 
> The mmap and mremap syscalls do not currently accept tagged addresses.
> Architectures may interpret the tag as a background colour for the
> corresponding vma.
> 
> Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  mm/madvise.c   | 2 ++
>  mm/mempolicy.c | 3 +++
>  mm/migrate.c   | 2 +-
>  mm/mincore.c   | 2 ++
>  mm/mlock.c     | 4 ++++
>  mm/mprotect.c  | 2 ++
>  mm/mremap.c    | 7 +++++++
>  mm/msync.c     | 2 ++
>  8 files changed, 23 insertions(+), 1 deletion(-)

More back and forth discussions on how to specify the exceptions here.
I'm proposing just dropping the exceptions and folding in the diff
below.

Andrew, if you prefer a standalone patch instead, please let me know:

------------------8<----------------------------
>From 9a5286acaa638c6a917d96986bf28dad35e24a0c Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@....com>
Date: Fri, 9 Aug 2019 14:21:33 +0100
Subject: [PATCH] fixup! mm: untag user pointers passed to memory syscalls

mmap, mremap, munmap, brk added to the list of syscalls that accept
tagged pointers.

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
 mm/mmap.c   | 5 +++++
 mm/mremap.c | 6 +-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 7e8c3e8ae75f..b766b633b7ae 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -201,6 +201,8 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 	bool downgraded = false;
 	LIST_HEAD(uf);
 
+	brk = untagged_addr(brk);
+
 	if (down_write_killable(&mm->mmap_sem))
 		return -EINTR;
 
@@ -1573,6 +1575,8 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
 	struct file *file = NULL;
 	unsigned long retval;
 
+	addr = untagged_addr(addr);
+
 	if (!(flags & MAP_ANONYMOUS)) {
 		audit_mmap_fd(fd, flags);
 		file = fget(fd);
@@ -2874,6 +2878,7 @@ EXPORT_SYMBOL(vm_munmap);
 
 SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
 {
+	addr = untagged_addr(addr);
 	profile_munmap(addr);
 	return __vm_munmap(addr, len, true);
 }
diff --git a/mm/mremap.c b/mm/mremap.c
index 64c9a3b8be0a..1fc8a29fbe3f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -606,12 +606,8 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	LIST_HEAD(uf_unmap_early);
 	LIST_HEAD(uf_unmap);
 
-	/*
-	 * Architectures may interpret the tag passed to mmap as a background
-	 * colour for the corresponding vma. For mremap we don't allow tagged
-	 * new_addr to preserve similar behaviour to mmap.
-	 */
 	addr = untagged_addr(addr);
+	new_addr = untagged_addr(new_addr);
 
 	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 		return ret;