From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marco Elver Subject: Re: [PATCH 2/3] x86: Move CPU feature test out of uaccess region Date: Fri, 31 May 2019 11:57:36 +0200 Message-ID: References: <20190529141500.193390-1-elver@google.com> <20190529141500.193390-3-elver@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "H. Peter Anvin" Cc: Peter Zijlstra , Andrey Ryabinin , Dmitry Vyukov , Alexander Potapenko , Andrey Konovalov , Mark Rutland , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , the arch/x86 maintainers , Arnd Bergmann , Josh Poimboeuf , "open list:DOCUMENTATION" , LKML , linux-arch , kasan-dev List-Id: linux-arch.vger.kernel.org On Wed, 29 May 2019 at 16:29, wrote: > > On May 29, 2019 7:15:00 AM PDT, Marco Elver wrote: > >This patch is a pre-requisite for enabling KASAN bitops > >instrumentation: > >moves boot_cpu_has feature test out of the uaccess region, as > >boot_cpu_has uses test_bit. With instrumentation, the KASAN check would > >otherwise be flagged by objtool. > > > >This approach is preferred over adding the explicit kasan_check_* > >functions to the uaccess whitelist of objtool, as the case here appears > >to be the only one. > > > >Signed-off-by: Marco Elver > >--- > >v1: > >* This patch replaces patch: 'tools/objtool: add kasan_check_* to > > uaccess whitelist' > >--- > > arch/x86/ia32/ia32_signal.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > >diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c > >index 629d1ee05599..12264e3c9c43 100644 > >--- a/arch/x86/ia32/ia32_signal.c > >+++ b/arch/x86/ia32/ia32_signal.c > >@@ -333,6 +333,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal > >*ksig, > > void __user *restorer; > > int err = 0; > > void __user *fpstate = NULL; > >+ bool has_xsave; > > > > /* __copy_to_user optimizes that into a single 8 byte store */ > > static const struct { > >@@ -352,13 +353,19 @@ int ia32_setup_rt_frame(int sig, struct ksignal > >*ksig, > > if (!access_ok(frame, sizeof(*frame))) > > return -EFAULT; > > > >+ /* > >+ * Move non-uaccess accesses out of uaccess region if not strictly > >+ * required; this also helps avoid objtool flagging these accesses > >with > >+ * instrumentation enabled. > >+ */ > >+ has_xsave = boot_cpu_has(X86_FEATURE_XSAVE); > > put_user_try { > > put_user_ex(sig, &frame->sig); > > put_user_ex(ptr_to_compat(&frame->info), &frame->pinfo); > > put_user_ex(ptr_to_compat(&frame->uc), &frame->puc); > > > > /* Create the ucontext. */ > >- if (boot_cpu_has(X86_FEATURE_XSAVE)) > >+ if (has_xsave) > > put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags); > > else > > put_user_ex(0, &frame->uc.uc_flags); > > This was meant to use static_cpu_has(). Why did that get dropped? I couldn't find any mailing list thread referring to why this doesn't use static_cpu_has, do you have any background? static_cpu_has also solves the UACCESS warning. If you confirm it is safe to change to static_cpu_has(), I will change this patch. Note that I should then also change arch/x86/kernel/signal.c to mirror the change for 32bit (although KASAN is not supported for 32bit x86). Thanks, -- Marco From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-f196.google.com ([209.85.167.196]:38700 "EHLO mail-oi1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726002AbfEaJ5s (ORCPT ); Fri, 31 May 2019 05:57:48 -0400 Received: by mail-oi1-f196.google.com with SMTP id 18so6482547oij.5 for ; Fri, 31 May 2019 02:57:47 -0700 (PDT) MIME-Version: 1.0 References: <20190529141500.193390-1-elver@google.com> <20190529141500.193390-3-elver@google.com> In-Reply-To: From: Marco Elver Date: Fri, 31 May 2019 11:57:36 +0200 Message-ID: Subject: Re: [PATCH 2/3] x86: Move CPU feature test out of uaccess region Content-Type: text/plain; charset="UTF-8" Sender: linux-arch-owner@vger.kernel.org List-ID: To: "H. Peter Anvin" Cc: Peter Zijlstra , Andrey Ryabinin , Dmitry Vyukov , Alexander Potapenko , Andrey Konovalov , Mark Rutland , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , the arch/x86 maintainers , Arnd Bergmann , Josh Poimboeuf , "open list:DOCUMENTATION" , LKML , linux-arch , kasan-dev Message-ID: <20190531095736.1yNweGwZ5duC2_Hm4W4RZYsjaE-POpw9Ao_R6uzBwwo@z> On Wed, 29 May 2019 at 16:29, wrote: > > On May 29, 2019 7:15:00 AM PDT, Marco Elver wrote: > >This patch is a pre-requisite for enabling KASAN bitops > >instrumentation: > >moves boot_cpu_has feature test out of the uaccess region, as > >boot_cpu_has uses test_bit. With instrumentation, the KASAN check would > >otherwise be flagged by objtool. > > > >This approach is preferred over adding the explicit kasan_check_* > >functions to the uaccess whitelist of objtool, as the case here appears > >to be the only one. > > > >Signed-off-by: Marco Elver > >--- > >v1: > >* This patch replaces patch: 'tools/objtool: add kasan_check_* to > > uaccess whitelist' > >--- > > arch/x86/ia32/ia32_signal.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > >diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c > >index 629d1ee05599..12264e3c9c43 100644 > >--- a/arch/x86/ia32/ia32_signal.c > >+++ b/arch/x86/ia32/ia32_signal.c > >@@ -333,6 +333,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal > >*ksig, > > void __user *restorer; > > int err = 0; > > void __user *fpstate = NULL; > >+ bool has_xsave; > > > > /* __copy_to_user optimizes that into a single 8 byte store */ > > static const struct { > >@@ -352,13 +353,19 @@ int ia32_setup_rt_frame(int sig, struct ksignal > >*ksig, > > if (!access_ok(frame, sizeof(*frame))) > > return -EFAULT; > > > >+ /* > >+ * Move non-uaccess accesses out of uaccess region if not strictly > >+ * required; this also helps avoid objtool flagging these accesses > >with > >+ * instrumentation enabled. > >+ */ > >+ has_xsave = boot_cpu_has(X86_FEATURE_XSAVE); > > put_user_try { > > put_user_ex(sig, &frame->sig); > > put_user_ex(ptr_to_compat(&frame->info), &frame->pinfo); > > put_user_ex(ptr_to_compat(&frame->uc), &frame->puc); > > > > /* Create the ucontext. */ > >- if (boot_cpu_has(X86_FEATURE_XSAVE)) > >+ if (has_xsave) > > put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags); > > else > > put_user_ex(0, &frame->uc.uc_flags); > > This was meant to use static_cpu_has(). Why did that get dropped? I couldn't find any mailing list thread referring to why this doesn't use static_cpu_has, do you have any background? static_cpu_has also solves the UACCESS warning. If you confirm it is safe to change to static_cpu_has(), I will change this patch. Note that I should then also change arch/x86/kernel/signal.c to mirror the change for 32bit (although KASAN is not supported for 32bit x86). Thanks, -- Marco