Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory syscalls

[Kees Cook <keescook@chromium.org>]

On Mon, Jun 03, 2019 at 06:55:07PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends arm64 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.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  mm/madvise.c   | 2 ++
>  mm/mempolicy.c | 3 +++
>  mm/mincore.c   | 2 ++
>  mm/mlock.c     | 4 ++++
>  mm/mprotect.c  | 2 ++
>  mm/mremap.c    | 2 ++
>  mm/msync.c     | 2 ++
>  7 files changed, 17 insertions(+)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 628022e674a7..39b82f8a698f 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -810,6 +810,8 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
>  	size_t len;
>  	struct blk_plug plug;
>  
> +	start = untagged_addr(start);
> +
>  	if (!madvise_behavior_valid(behavior))
>  		return error;
>  
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 01600d80ae01..78e0a88b2680 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1360,6 +1360,7 @@ static long kernel_mbind(unsigned long start, unsigned long len,
>  	int err;
>  	unsigned short mode_flags;
>  
> +	start = untagged_addr(start);
>  	mode_flags = mode & MPOL_MODE_FLAGS;
>  	mode &= ~MPOL_MODE_FLAGS;
>  	if (mode >= MPOL_MAX)
> @@ -1517,6 +1518,8 @@ static int kernel_get_mempolicy(int __user *policy,
>  	int uninitialized_var(pval);
>  	nodemask_t nodes;
>  
> +	addr = untagged_addr(addr);
> +
>  	if (nmask != NULL && maxnode < nr_node_ids)
>  		return -EINVAL;
>  
> diff --git a/mm/mincore.c b/mm/mincore.c
> index c3f058bd0faf..64c322ed845c 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -249,6 +249,8 @@ SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
>  	unsigned long pages;
>  	unsigned char *tmp;
>  
> +	start = untagged_addr(start);
> +
>  	/* Check the start address: needs to be page-aligned.. */
>  	if (start & ~PAGE_MASK)
>  		return -EINVAL;
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 080f3b36415b..e82609eaa428 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -674,6 +674,8 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>  	unsigned long lock_limit;
>  	int error = -ENOMEM;
>  
> +	start = untagged_addr(start);
> +
>  	if (!can_do_mlock())
>  		return -EPERM;
>  
> @@ -735,6 +737,8 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
>  {
>  	int ret;
>  
> +	start = untagged_addr(start);
> +
>  	len = PAGE_ALIGN(len + (offset_in_page(start)));
>  	start &= PAGE_MASK;
>  
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index bf38dfbbb4b4..19f981b733bc 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -465,6 +465,8 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
>  	const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
>  				(prot & PROT_READ);
>  
> +	start = untagged_addr(start);
> +
>  	prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
>  	if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
>  		return -EINVAL;
> diff --git a/mm/mremap.c b/mm/mremap.c
> index fc241d23cd97..1d98281f7204 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -606,6 +606,8 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
>  	LIST_HEAD(uf_unmap_early);
>  	LIST_HEAD(uf_unmap);
>  
> +	addr = untagged_addr(addr);
> +
>  	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
>  		return ret;
>  
> diff --git a/mm/msync.c b/mm/msync.c
> index ef30a429623a..c3bd3e75f687 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -37,6 +37,8 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
>  	int unmapped_error = 0;
>  	int error = -EINVAL;
>  
> +	start = untagged_addr(start);
> +
>  	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
>  		goto out;
>  	if (offset_in_page(start))
> -- 
> 2.22.0.rc1.311.g5d7573a151-goog
> 

-- 
Kees Cook