linux-kernel - Re: [git pull] uaccess-related bits of vfs.git

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Message-ID: <20170513191142.GB390@ZenIV.linux.org.uk>
Date:   Sat, 13 May 2017 20:11:42 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [git pull] uaccess-related bits of vfs.git

On Sat, May 13, 2017 at 07:26:56PM +0100, Al Viro wrote:
> BTW, even in arch/* they tend to nest.  E.g. arch/alpha has 133 callers
> total.  Distribution by files:
>      35 arch/alpha/kernel/osf_sys.c
>      92 arch/alpha/kernel/signal.c
>       1 arch/alpha/kernel/traps.c
>       4 arch/alpha/lib/csum_partial_copy.c
>       1 arch/alpha/mm/fault.c

Another large pile is on sparc (208 callers).  Except that on sparc64
access_ok() is constant 1, which reduces it to 42 callers.
        3 arch/sparc/kernel/ptrace_32.c (all in arch_ptrace())
       31 arch/sparc/kernel/signal_32.c (5 in do_sigreturn(),
					 6 in do_rt_sigreturn(),
					 8 in setup_frame(),
					 11 in setup_rt_frame(),
					 1 in do_sys_sigstack())
	7 arch/sparc/kernel/sigutil_32.c (2 in save_fpu_state(),
					  2 in restore_fpu_state(),
					  2 in save_rwin_state(),
					  1 in restore_rwin_state()
	1 arch/sparc/mm/fault_32.c (in compute_si_addr())

The last one ignores -EFAULT, BTW - not sure what should it have done
in that case, though.  It's calculation of ->si_addr on SIGSEGV and SIGBUS
in case of data access SIGSEGV or SIGBUS; it wants to peek into insn to
figure out the effective address.  arch_ptrace() one is zeroing several
fields in userland struct fps for PTRACE_GETFPREGS.  Could've been
put_user() (or clear_user(), for that matter); we'd just done
copy_regset_to_user() on adjacent addresses, so the lack of access_ok() is not
a security hole there).  Everything else is in sigframe handling...

Other large piles are on mips, ppc and itanic.  parisc is next, but there
access_ok() is constant 1 as well.  Same for s390 and m68k.  nios2 and
unicore32 are a bit under 80 callers each and the next are tile (~60),
sh (~50) and then it drops off fast.

It's not impossible to review; the problem is in figuring out which codepaths
are hot enough to worry about them.  And I'm even more convinced that
bulk search-and-replace is the right approach here; we probably _can_ get
rid of that shit this cycle (or, at least, reduce its use to very few places
in arch/*), but that'll require some cooperation from architecture maintainers.