From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vincenzo Frascino Subject: Re: [PATCH v16 02/16] arm64: untag user pointers in access_ok and __uaccess_mask_ptr Date: Wed, 12 Jun 2019 12:52:49 +0100 Message-ID: References: <4327b260fb17c4776a1e3c844f388e4948cfb747.1559580831.git.andreyknvl@google.com> <20190610175326.GC25803@arrakis.emea.arm.com> <20190611145720.GA63588@arrakis.emea.arm.com> <20190612093158.GG10165@c02tf0j2hf1t.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190612093158.GG10165@c02tf0j2hf1t.cambridge.arm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Catalin Marinas Cc: Andrey Konovalov , Mark Rutland , kvm@vger.kernel.org, Szabolcs Nagy , Will Deacon , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Khalid Aziz , linux-kselftest@vger.kernel.org, Felix Kuehling , Jacob Bramley , Leon Romanovsky , linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org, Christoph Hellwig , Jason Gunthorpe , Dmitry Vyukov , Dave Martin , Evgeniy Stepanov , linux-media@vger.kernel.org, Kevin Brodsky , Kees Cook List-Id: linux-rdma@vger.kernel.org Hi Catalin, On 12/06/2019 10:32, Catalin Marinas wrote: > Hi Vincenzo, > > On Tue, Jun 11, 2019 at 06:09:10PM +0100, Vincenzo Frascino wrote: >>> 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 >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -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); >> >> Nit: in line we the other functions in thread_flush we could have something like >> "tagged_addr_thread_flush", maybe inlined. > > The other functions do a lot more than clearing a TIF flag, so they > deserved their own place. We could do this when adding MTE support. I > think we also need to check what other TIF flags we may inadvertently > pass on execve(), maybe have a mask clearing. > Agreed. All the comments I provided are meant to simplify the addition of MTE support. >>> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h >>> index 094bb03b9cc2..2e927b3e9d6c 100644 >>> --- a/include/uapi/linux/prctl.h >>> +++ b/include/uapi/linux/prctl.h >>> @@ -229,4 +229,9 @@ struct prctl_mm_map { >>> # define PR_PAC_APDBKEY (1UL << 3) >>> # define PR_PAC_APGAKEY (1UL << 4) >>> >>> +/* Tagged user address controls for arm64 */ >>> +#define PR_SET_TAGGED_ADDR_CTRL 55 >>> +#define PR_GET_TAGGED_ADDR_CTRL 56 >>> +# define PR_TAGGED_ADDR_ENABLE (1UL << 0) >>> + >>> #endif /* _LINUX_PRCTL_H */ >>> diff --git a/kernel/sys.c b/kernel/sys.c >>> index 2969304c29fe..ec48396b4943 100644 >>> --- a/kernel/sys.c >>> +++ b/kernel/sys.c >>> @@ -124,6 +124,12 @@ >>> #ifndef PAC_RESET_KEYS >>> # define PAC_RESET_KEYS(a, b) (-EINVAL) >>> #endif >>> +#ifndef SET_TAGGED_ADDR_CTRL >>> +# define SET_TAGGED_ADDR_CTRL(a) (-EINVAL) >>> +#endif >>> +#ifndef GET_TAGGED_ADDR_CTRL >>> +# define GET_TAGGED_ADDR_CTRL() (-EINVAL) >>> +#endif >>> >>> /* >>> * this is where the system-wide overflow UID and GID are defined, for >>> @@ -2492,6 +2498,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, >>> return -EINVAL; >>> error = PAC_RESET_KEYS(me, arg2); >>> break; >>> + case PR_SET_TAGGED_ADDR_CTRL: >>> + if (arg3 || arg4 || arg5) >>> + return -EINVAL; >>> + error = SET_TAGGED_ADDR_CTRL(arg2); >>> + break; >>> + case PR_GET_TAGGED_ADDR_CTRL: >>> + if (arg2 || arg3 || arg4 || arg5) >>> + return -EINVAL; >>> + error = GET_TAGGED_ADDR_CTRL(); >>> + break; >> >> Why do we need two prctl here? We could have only one and use arg2 as set/get >> and arg3 as a parameter. What do you think? > > This follows the other PR_* options, e.g. PR_SET_VL/GET_VL, > PR_*_FP_MODE. We will use other bits in arg2, for example to set the > precise vs imprecise MTE trapping. > Indeed. I was not questioning the pre-existing interface definition, but trying more to reduce the changes to the ABI to the minimum since: - prctl does not mandate how to use the arg[2-5] - prctl interface is flexible enough for the problem to be solved with only one PR_ command. I agree on reusing the interface for MTE for the purposes you specified. -- Regards, Vincenzo