linux-kernel - Re: [PATCH v2] arm64: kprobe: make page to RO mode when allocate it

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Message-ID: <20181102174051.GH218059@arrakis.emea.arm.com>
Date:   Fri, 2 Nov 2018 17:40:51 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] arm64: kprobe: make page to RO mode when allocate it

On Tue, Oct 30, 2018 at 11:10:51AM -0300, Ard Biesheuvel wrote:
> On 30 October 2018 at 08:49, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> >> On 30 Oct 2018, at 08:38, Anders Roxell <anders.roxell@...aro.org> wrote:
> >>
> >> Commit 1404d6f13e47 ("arm64: dump: Add checking for writable and exectuable pages")
> >> has successfully identified code that leaves a page with W+X
> >> permissions.
> >>
> >> [    3.245140] arm64/mm: Found insecure W+X mapping at address (____ptrval____)/0xffff000000d90000
> >> [    3.245771] WARNING: CPU: 0 PID: 1 at ../arch/arm64/mm/dump.c:232 note_page+0x410/0x420
> >> [    3.246141] Modules linked in:
> >> [    3.246653] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc5-next-20180928-00001-ge70ae259b853-dirty #62
> >> [    3.247008] Hardware name: linux,dummy-virt (DT)
> >> [    3.247347] pstate: 80000005 (Nzcv daif -PAN -UAO)
> >> [    3.247623] pc : note_page+0x410/0x420
> >> [    3.247898] lr : note_page+0x410/0x420
> >> [    3.248071] sp : ffff00000804bcd0
> >> [    3.248254] x29: ffff00000804bcd0 x28: ffff000009274000
> >> [    3.248578] x27: ffff00000921a000 x26: ffff80007dfff000
> >> [    3.248845] x25: ffff0000093f5000 x24: ffff000009526f6a
> >> [    3.249109] x23: 0000000000000004 x22: ffff000000d91000
> >> [    3.249396] x21: ffff000000d90000 x20: 0000000000000000
> >> [    3.249661] x19: ffff00000804bde8 x18: 0000000000000400
> >> [    3.249924] x17: 0000000000000000 x16: 0000000000000000
> >> [    3.250271] x15: ffffffffffffffff x14: 295f5f5f5f6c6176
> >> [    3.250594] x13: 7274705f5f5f5f28 x12: 2073736572646461
> >> [    3.250941] x11: 20746120676e6970 x10: 70616d20582b5720
> >> [    3.251252] x9 : 6572756365736e69 x8 : 3039643030303030
> >> [    3.251519] x7 : 306666666678302f x6 : ffff0000095467b2
> >> [    3.251802] x5 : 0000000000000000 x4 : 0000000000000000
> >> [    3.252060] x3 : 0000000000000000 x2 : ffffffffffffffff
> >> [    3.252323] x1 : 4d151327adc50b00 x0 : 0000000000000000
> >> [    3.252664] Call trace:
> >> [    3.252953]  note_page+0x410/0x420
> >> [    3.253186]  walk_pgd+0x12c/0x238
> >> [    3.253417]  ptdump_check_wx+0x68/0xf8
> >> [    3.253637]  mark_rodata_ro+0x68/0x98
> >> [    3.253847]  kernel_init+0x38/0x160
> >> [    3.254103]  ret_from_fork+0x10/0x18
> >>
> >> kprobes allocates a writable executable page with module_alloc() in
> >> order to store executable code.
> >> Reworked to that when allocate a page it sets mode RO. Inspired by
> >> commit 63fef14fc98a ("kprobes/x86: Make insn buffer always ROX and use text_poke()").
> >>
> >> Cc: Laura Abbott <labbott@...hat.com>
> >> Cc: Catalin Marinas <catalin.marinas@....com>
> >> Co-developed-by: Arnd Bergmann <arnd@...db.de>
> >> Co-developed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> >> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> >
> > Please remove these SOBs, Arnd and I provided input to this patch
> > but you are the one sending it (sob does not assert authorship or
> > anything like that, it just asserts that the code in the patch was
> > made available under a compatible license)
> 
> As Anders points out in a private communication, the Documentation/
> explicitly requires signoffs for Co-developed-by credits. Perhaps we
> should enhance that document to clarify that that does not mean you
> can simply add signoffs on someone else's behalf.

I think I'll rename co-developed-by with suggested-by to keep things
simpler. Are you ok with this (or are you providing an explicit
signed-off-by)?

-- 
Catalin