From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 18DBC28C5CD; Wed, 28 May 2025 17:24:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748453083; cv=none; b=AiC2w+JIRfSTpMyztlQ3vI5WShqQoYODoPAOrgDTXyn75hnOO85XLWbrsEJNKUdk9ucScikHIs6leCc6umrh47SVOV4+pm6SI5o6+WzQg/rkIbPmawVP0oxkb4o4v1mLmUpMQlc/GNzrH6KswPkEeuC8IHktLtfcwbgb0hjTN6U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748453083; c=relaxed/simple; bh=xl+HiA5fKcIkxj9tC9RYJv/z6ok1+kvXmKS4mrZe1yQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K/7b5z233U5Tt592hNx5y2EulxNz59FeMLVtQRCDEKx8ssBNU5FLhRwB0KXV8T6U4uPy+DoCnHB03dT/BTa5kN2wYML9xRLDqgS53GwSY6LaN5ijPGr3FAiuk2+Yk6AB969rNOPYpWVmNI19CIlt6IW2WePd1K2I8KJ/w6b52Ok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kQGDWWY4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kQGDWWY4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07719C4CEED; Wed, 28 May 2025 17:24:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748453082; bh=xl+HiA5fKcIkxj9tC9RYJv/z6ok1+kvXmKS4mrZe1yQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kQGDWWY4RxXpI1BJNG3aGyloC7hTGfN72V52PM8GHltRqJcyj3kH2JlCT0ocipFXM gYawpFMlZwcpPMnN2awtU+odn01+CYDC/TfVacqWqvDrGeImfGEMd1a2VcAtkkTr+1 PWgxHD4JUWE2Ngzsu7yeipX2hr90I81H3Kxf5jnLyO5UmkrpGdltIXqJvGITFz8pKu rloqohx8uszXcdHIYJR4F8QXX6bLRVBblNBgPuT7F57aNecC0agUmrlqHG3f45J9xw 4Pd1F1nDW4QSDPngOLDYzHTpNcfsaTxvwbikvscuRi4lsYDhmCrbaghoIKE5vr8NFj L2jYeoGheanBw== Date: Wed, 28 May 2025 20:24:35 +0300 From: Mike Rapoport To: Peter Zijlstra Cc: =?iso-8859-1?Q?J=FCrgen_Gro=DF?= , linux-kernel@vger.kernel.org, x86@kernel.org, xin@zytor.com, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , stable@vger.kernel.org Subject: Re: [PATCH 3/3] x86/alternative: make kernel ITS thunks read-only Message-ID: References: <20250528123557.12847-1-jgross@suse.com> <20250528123557.12847-4-jgross@suse.com> <20250528131052.GZ39944@noisy.programming.kicks-ass.net> <044f0048-95bb-4822-978e-a23528f3891f@suse.com> <20250528132231.GB39944@noisy.programming.kicks-ass.net> <7c8bf4f5-29a0-4147-b31a-5e420b11468e@suse.com> <20250528155821.GD39944@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250528155821.GD39944@noisy.programming.kicks-ass.net> On Wed, May 28, 2025 at 05:58:21PM +0200, Peter Zijlstra wrote: > On Wed, May 28, 2025 at 03:30:33PM +0200, Jürgen Groß wrote: > > > Have a look at its_fini_mod(). > > Oh, that's what you mean. But this still isn't very nice, you now have > restore_rox() without make_temp_rw(), which was the intended usage > pattern. > > Bah, I hate how execmem works different for !PSE, Mike, you see a sane > way to fix this? Not really :( But just resetting permissions in the end like you did makes perfect sense to me. It's like STRICT_MODULE_RWX, somebody has to set the pages to ROX at some point and running execmem_restore_rox() on something that was already ROX won't cost much, set_memory will bail out early. > Anyway, if we have to do something like this, then I would prefer it > shaped something like so: > > --- > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index ecfe7b497cad..33d4d139cb50 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -111,9 +111,8 @@ static bool cfi_paranoid __ro_after_init; > > #ifdef CONFIG_MITIGATION_ITS > > -#ifdef CONFIG_MODULES > static struct module *its_mod; > -#endif > +static struct its_array its_pages; > static void *its_page; > static unsigned int its_offset; > > @@ -151,68 +150,78 @@ static void *its_init_thunk(void *thunk, int reg) > return thunk + offset; > } > > -#ifdef CONFIG_MODULES > void its_init_mod(struct module *mod) > { > if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS)) > return; > > - mutex_lock(&text_mutex); > - its_mod = mod; > - its_page = NULL; > + if (mod) { > + mutex_lock(&text_mutex); > + its_mod = mod; > + its_page = NULL; > + } > } > > void its_fini_mod(struct module *mod) > { > + struct its_array *pages = &its_pages; > + > if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS)) > return; > > WARN_ON_ONCE(its_mod != mod); > > - its_mod = NULL; > - its_page = NULL; > - mutex_unlock(&text_mutex); > + if (mod) { > + pages = &mod->arch.its_pages; > + its_mod = NULL; > + its_page = NULL; > + mutex_unlock(&text_mutex); > + } > > - for (int i = 0; i < mod->its_num_pages; i++) { > - void *page = mod->its_page_array[i]; > + for (int i = 0; i < pages->num; i++) { > + void *page = pages->pages[i]; > execmem_restore_rox(page, PAGE_SIZE); > } > + > + if (!mod) > + kfree(pages->pages); > } > > void its_free_mod(struct module *mod) > { > + struct its_array *pages = &its_pages; > + > if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS)) > return; > > - for (int i = 0; i < mod->its_num_pages; i++) { > - void *page = mod->its_page_array[i]; > + if (mod) > + pages = &mod->arch.its_pages; > + > + for (int i = 0; i < pages->num; i++) { > + void *page = pages->pages[i]; > execmem_free(page); > } > - kfree(mod->its_page_array); > + kfree(pages->pages); > } > -#endif /* CONFIG_MODULES */ > > static void *its_alloc(void) > { > - void *page __free(execmem) = execmem_alloc(EXECMEM_MODULE_TEXT, PAGE_SIZE); > + struct its_array *pages = &its_pages; > + void *tmp; > > + void *page __free(execmem) = execmem_alloc(EXECMEM_MODULE_TEXT, PAGE_SIZE); > if (!page) > return NULL; > > -#ifdef CONFIG_MODULES > - if (its_mod) { > - void *tmp = krealloc(its_mod->its_page_array, > - (its_mod->its_num_pages+1) * sizeof(void *), > - GFP_KERNEL); > - if (!tmp) > - return NULL; > + tmp = krealloc(pages->pages, (pages->num + 1) * sizeof(void *), GFP_KERNEL); > + if (!tmp) > + return NULL; > > - its_mod->its_page_array = tmp; > - its_mod->its_page_array[its_mod->its_num_pages++] = page; > + pages->pages = tmp; > + pages->pages[pages->num++] = page; > > + if (its_mod) > execmem_make_temp_rw(page, PAGE_SIZE); > - } > -#endif /* CONFIG_MODULES */ > > return no_free_ptr(page); > } > @@ -2338,6 +2347,8 @@ void __init alternative_instructions(void) > apply_retpolines(__retpoline_sites, __retpoline_sites_end); > apply_returns(__return_sites, __return_sites_end); > > + its_fini_mod(NULL); > + > /* > * Adjust all CALL instructions to point to func()-10, including > * those in .altinstr_replacement. -- Sincerely yours, Mike.