On 10/17/23 2:08 PM, jef...@chromium.org wrote:
> From: Jeff Xu <jef...@google.com>
>
> mremap(2) can shrink/expand a VMA, or move a VMA to a fixed
> address and overwriting or existing VMA. Sealing will
> prevent unintended mremap(2) call.
>
> What this patch does:
> When a mremap(2) is invoked, if one of its VMAs has MM_SEAL_MREMAP
> set from previous mseal(2) call, this mremap(2) will fail, without
> any VMA modified.
>
> This patch is based on following:
> 1. At syscall entry point: SYSCALL_DEFINE5(mremap,...)
> There are two cases:
Maybe we can reduce the code duplication by bringing the check if memory is
sealed before call to mremap_to().
> a. going into mremap_to().
> b. not going into mremap_to().
>
> 2. For mremap_to() case.
> Since mremap_to() is called only from SYSCALL_DEFINE5(mremap,..),
> omit changing signature of mremap_to(), i.e. not passing
> checkSeals flag.
> In mremap_to(), it calls can_modify_mm() for src address and
> dst address (when MREMAP_FIXED is used), before any update is
> made to the VMAs.
>
> 3. For non mremap_to() case.
> It is still part of SYSCALL_DEFINE5(mremap,...).
> It calls can_modify_mm() to check sealing in the src address,
> before any update is made to src VMAs.
> Check for dest address is not needed, because dest memory is
> allocated in current mremap(2) call.
>
> Signed-off-by: Jeff Xu <jef...@google.com>
> ---
> mm/mremap.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index ac363937f8c4..691fc32d37e4 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -836,7 +836,27 @@ static unsigned long mremap_to(unsigned long addr,
> unsigned long old_len,
> if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
> return -ENOMEM;
>
> + /*
> + * Check src address for sealing.
> + *
> + * Note: mremap_to() currently called from one place:
> + * SYSCALL_DEFINE4(pkey_mprotect, ...)
> + * and not in any other places.
> + * Therefore, omit changing the signature of mremap_to()
> + * Otherwise, we might need to add checkSeals and pass it
> + * from all callers of mremap_to().
> + */
> + if (!can_modify_mm(mm, addr, addr + old_len, MM_SEAL_MREMAP))
> + return -EACCES;
> +
> if (flags & MREMAP_FIXED) {
> + /*
> + * Check dest address for sealing.
> + */
> + if (!can_modify_mm(mm, new_addr, new_addr + new_len,
> + MM_SEAL_MREMAP))
> + return -EACCES;
> +
Move these two checks to just before call to mremap_to() in sys_mremap() or
even earlier. Or even better move the first condition before mremap_to()
and second condition can be checked before call to mremap_to().
> ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
> if (ret)
> goto out;
> @@ -995,6 +1015,11 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned
> long, old_len,
> goto out;
> }
>
> + if (!can_modify_mm(mm, addr, addr + old_len, MM_SEAL_MREMAP)) {
> + ret = -EACCES;
> + goto out;
> + }
> +
> /*
> * Always allow a shrinking remap: that just unmaps
> * the unnecessary pages..
--
BR,
Muhammad Usama Anjum
