On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > process_madvise currently requires ptrace attach capability. > PTRACE_MODE_ATTACH gives one process complete control over another > process. It effectively removes the security boundary between the > two processes (in one direction). Granting ptrace attach capability > even to a system process is considered dangerous since it creates an > attack surface. This severely limits the usage of this API. > The operations process_madvise can perform do not affect the correctness > of the operation of the target process; they only affect where the data > is physically located (and therefore, how fast it can be accessed). > What we want is the ability for one process to influence another process > in order to optimize performance across the entire system while leaving > the security boundary intact. > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > and CAP_SYS_NICE for influencing process performance. > > Cc: stable@xxxxxxxxxxxxxxx # 5.10+ > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > --- > changes in v3 > - Added Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f458bad476a3358e3a45023789cb7bb9f993 > - cc'ed stable@xxxxxxxxxxxxxxx # 5.10+ per Andrew's request > - cc'ed linux-security-module@xxxxxxxxxxxxxxx per James Morris's request > > mm/madvise.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index df692d2e35d4..01fef79ac761 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > goto release_task; > } > > - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); > + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ > + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); > if (IS_ERR_OR_NULL(mm)) { > ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; > goto release_task; > } > > + /* > + * Require CAP_SYS_NICE for influencing process performance. Note that > + * only non-destructive hints are currently supported. How is non-destructive defined? Is MADV_DONTNEED non-destructive? > + */ > + if (!capable(CAP_SYS_NICE)) { > + ret = -EPERM; > + goto release_mm; > + } > + > total_len = iov_iter_count(&iter); > > while (iov_iter_count(&iter)) { > @@ -1218,6 +1228,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > if (ret == 0) > ret = total_len - iov_iter_count(&iter); > > +release_mm: > mmput(mm); > release_task: > put_task_struct(task); > -- > 2.30.1.766.gb4fecdf3b7-goog >
