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Date: Thu, 13 Jun 2019 16:35:07 +0100 From: Catalin Marinas <catalin.marinas@....com> To: Dave Martin <Dave.Martin@....com> Cc: Andrey Konovalov <andreyknvl@...gle.com>, linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org, linux-media@...r.kernel.org, kvm@...r.kernel.org, linux-kselftest@...r.kernel.org, Mark Rutland <mark.rutland@....com>, Szabolcs Nagy <Szabolcs.Nagy@....com>, Will Deacon <will.deacon@....com>, Kostya Serebryany <kcc@...gle.com>, Khalid Aziz <khalid.aziz@...cle.com>, Felix Kuehling <Felix.Kuehling@....com>, Vincenzo Frascino <vincenzo.frascino@....com>, Jacob Bramley <Jacob.Bramley@....com>, Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@...radead.org>, Jason Gunthorpe <jgg@...pe.ca>, Evgeniy Stepanov <eugenis@...gle.com>, Kevin Brodsky <kevin.brodsky@....com>, Kees Cook <keescook@...omium.org>, Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>, Alex Williamson <alex.williamson@...hat.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Yishai Hadas <yishaih@...lanox.com>, Jens Wiklander <jens.wiklander@...aro.org>, Lee Smith <Lee.Smith@....com>, Alexander Deucher <Alexander.Deucher@....com>, Andrew Morton <akpm@...ux-foundation.org>, enh <enh@...gle.com>, Robin Murphy <robin.murphy@....com>, Christian Koenig <Christian.Koenig@....com>, Luc Van Oostenryck <luc.vanoostenryck@...il.com> Subject: Re: [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI On Thu, Jun 13, 2019 at 12:16:59PM +0100, Dave P Martin wrote: > On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote: > > From: Catalin Marinas <catalin.marinas@....com> > > > > It is not desirable to relax the ABI to allow tagged user addresses into > > the kernel indiscriminately. This patch introduces a prctl() interface > > for enabling or disabling the tagged ABI with a global sysctl control > > for preventing applications from enabling the relaxed ABI (meant for > > testing user-space prctl() return error checking without reconfiguring > > the kernel). The ABI properties are inherited by threads of the same > > application and fork()'ed children but cleared on execve(). > > > > The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle > > MTE-specific settings like imprecise vs precise exceptions. > > > > Signed-off-by: Catalin Marinas <catalin.marinas@....com> > > --- > > arch/arm64/include/asm/processor.h | 6 +++ > > arch/arm64/include/asm/thread_info.h | 1 + > > arch/arm64/include/asm/uaccess.h | 3 +- > > arch/arm64/kernel/process.c | 67 ++++++++++++++++++++++++++++ > > include/uapi/linux/prctl.h | 5 +++ > > kernel/sys.c | 16 +++++++ > > 6 files changed, 97 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > > index fcd0e691b1ea..fee457456aa8 100644 > > --- a/arch/arm64/include/asm/processor.h > > +++ b/arch/arm64/include/asm/processor.h > > @@ -307,6 +307,12 @@ extern void __init minsigstksz_setup(void); > > /* PR_PAC_RESET_KEYS prctl */ > > #define PAC_RESET_KEYS(tsk, arg) ptrauth_prctl_reset_keys(tsk, arg) > > > > +/* PR_TAGGED_ADDR prctl */ > > (A couple of comments I missed in my last reply:) > > Name mismatch? Yeah, it went through several names but it seems that I didn't update all places. > > +long set_tagged_addr_ctrl(unsigned long arg); > > +long get_tagged_addr_ctrl(void); > > +#define SET_TAGGED_ADDR_CTRL(arg) set_tagged_addr_ctrl(arg) > > +#define GET_TAGGED_ADDR_CTRL() get_tagged_addr_ctrl() > > + > > [...] > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index 3767fb21a5b8..69d0be1fc708 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -30,6 +30,7 @@ > > #include <linux/kernel.h> > > #include <linux/mm.h> > > #include <linux/stddef.h> > > +#include <linux/sysctl.h> > > #include <linux/unistd.h> > > #include <linux/user.h> > > #include <linux/delay.h> > > @@ -323,6 +324,7 @@ void flush_thread(void) > > fpsimd_flush_thread(); > > tls_thread_flush(); > > flush_ptrace_hw_breakpoint(current); > > + clear_thread_flag(TIF_TAGGED_ADDR); > > } > > > > void release_thread(struct task_struct *dead_task) > > @@ -552,3 +554,68 @@ void arch_setup_new_exec(void) > > > > ptrauth_thread_init_user(current); > > } > > + > > +/* > > + * Control the relaxed ABI allowing tagged user addresses into the kernel. > > + */ > > +static unsigned int tagged_addr_prctl_allowed = 1; > > + > > +long set_tagged_addr_ctrl(unsigned long arg) > > +{ > > + if (!tagged_addr_prctl_allowed) > > + return -EINVAL; > > So, tagging can actually be locked on by having a process enable it and > then some possibly unrelated process clearing tagged_addr_prctl_allowed. > That feels a bit weird. The problem is that if you disable the ABI globally, lots of applications would crash. This sysctl is meant as a way to disable the opt-in to the TBI ABI. Another option would be a kernel command line option (I'm not keen on a Kconfig option). > Do we want to allow a process that has tagging on to be able to turn > it off at all? Possibly things like CRIU might want to do that. I left it in for symmetry but I don't expect it to be used. A potential use-case is doing it per subsequent threads in an application. > > + if (is_compat_task()) > > + return -EINVAL; > > + if (arg & ~PR_TAGGED_ADDR_ENABLE) > > + return -EINVAL; > > How do we expect this argument to be extended in the future? Yes, for MTE. That's why I wouldn't allow random bits here. > I'm wondering whether this is really a bitmask or an enum, or a mixture > of the two. Maybe it doesn't matter. User may want to set PR_TAGGED_ADDR_ENABLE | PR_MTE_PRECISE in a single call. > > + if (arg & PR_TAGGED_ADDR_ENABLE) > > + set_thread_flag(TIF_TAGGED_ADDR); > > + else > > + clear_thread_flag(TIF_TAGGED_ADDR); > > I think update_thread_flag() could be used here. Yes. I forgot you added this. -- Catalin
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