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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfk9h-0001En-7h; Thu, 19 Nov 2020 13:39:21 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfk9e-0001ER-CA for linux-arm-kernel@lists.infradead.org; Thu, 19 Nov 2020 13:39:19 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0521C1042; Thu, 19 Nov 2020 05:39:16 -0800 (PST) Received: from [10.57.26.40] (unknown [10.57.26.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5F3AF3F718; Thu, 19 Nov 2020 05:39:15 -0800 (PST) Subject: Re: [RFC PATCH 1/2] arm64: Support execute-only permissions with Enhanced PAN To: Catalin Marinas References: <20201113152023.102855-1-vladimir.murzin@arm.com> <20201113152023.102855-2-vladimir.murzin@arm.com> <5e4cdc4a-d8be-6df7-e096-018cc3fe3463@arm.com> From: Vladimir Murzin Message-ID: <0a0f794f-d651-1b21-6ac3-a92d0f9d9420@arm.com> Date: Thu, 19 Nov 2020 13:39:15 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201119_083918_533116_8BE8AEA4 X-CRM114-Status: GOOD ( 28.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: keescook@chromium.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 11/18/20 4:04 PM, Catalin Marinas wrote: > On Wed, Nov 18, 2020 at 12:37:40PM +0000, Vladimir Murzin wrote: >> On 11/17/20 4:48 PM, Catalin Marinas wrote: >>> On Fri, Nov 13, 2020 at 03:20:22PM +0000, Vladimir Murzin wrote: >>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >>>> index 4ff12a7..d1f68d2 100644 >>>> --- a/arch/arm64/include/asm/pgtable.h >>>> +++ b/arch/arm64/include/asm/pgtable.h >>>> @@ -113,8 +113,15 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]; >>>> #define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte)) >>>> >>>> #define pte_valid(pte) (!!(pte_val(pte) & PTE_VALID)) >>>> -#define pte_valid_not_user(pte) \ >>>> - ((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID) >>>> +#define pte_valid_not_user(pte) \ >>>> +({ \ >>>> + int __val; \ >>>> + if (cpus_have_const_cap(ARM64_HAS_EPAN)) \ >>>> + __val = (pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN); \ >>>> + else \ >>>> + __val = (pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID; \ >>>> + __val; \ >>> >>> Is it worth having the cap check here? I'd go with the PTE_VALID|PTE_UXN >>> check only. >> >> I do not know to be honest. I do not have full picture in mind and >> what could be side effects of the change (that's why RFC). >> 24cecc377463 the PTE_VALID|PTE_UXN moved to PTE_VALID, so I decided to >> be safe than sorry... > > A user has access to a page if it has PTE_VALID && (PTE_USER || !PTE_UXN) > (wrong user of the logic operators but you get the idea). So negating > the user part in the above expression, pte_valid_not_user() means > PTE_VALID && !PTE_USER && PTE_UXN. > > Prior to these patches (or the old exec-only), we can't have PTE_UXN and > PTE_USER both cleared, this is introduced by PAGE_EXECONLY. IOW, without > EPAN, !PTE_USER implies PTE_UXN, so we can use the same check as for the > EPAN case. > >>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>>> index dcc165b..2033e0b 100644 >>>> --- a/arch/arm64/kernel/cpufeature.c >>>> +++ b/arch/arm64/kernel/cpufeature.c >>>> @@ -1602,6 +1602,13 @@ static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused) >>>> } >>>> #endif /* CONFIG_ARM64_PAN */ >>>> >>>> +#ifdef CONFIG_ARM64_EPAN >>>> +static void cpu_enable_epan(const struct arm64_cpu_capabilities *__unused) >>>> +{ >>>> + sysreg_clear_set(sctlr_el1, 0, SCTLR_EL1_EPAN); >>>> +} >>>> +#endif /* CONFIG_ARM64_EPAN */ >>> >>> I checked the spec (2020 arch updates) and the EPAN bit is permitted to >>> be cached in the TLB. I think we get away with this because this >>> function is called before cnp is enabled. Maybe we should make it >>> explicit and move the CnP entry last with a comment. >> >> Hmm, so we rely on CnP's enable method to (indirectly) involve >> local_flush_tlb_all()? It doesn't seem robust since CONFIG_ARM64_CNP >> could be unset. I can add local_flush_tlb_all() into cpu_enable_epan() >> or we can have something like > > A local_flush_tlb_all() in cpu_enable_epan() would be fine before user > space starts. However, a late CPU bring-up may cause a temporary > disabling of EPAN in the sibling core if CnP is enabled first. > >> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >> index bb2016c..0f0a27b 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -2416,6 +2416,8 @@ static int cpu_enable_non_boot_scope_capabilities(void *__unused) >> if (cap->cpu_enable) >> cap->cpu_enable(cap); >> } >> + >> + local_flush_tlb_all(); >> return 0; >> } >> >> @@ -2467,6 +2469,8 @@ static void __init enable_cpu_capabilities(u16 scope_mask) >> if (!boot_scope) >> stop_machine(cpu_enable_non_boot_scope_capabilities, >> NULL, cpu_online_mask); >> + else >> + local_flush_tlb_all(); >> } > > Any local TLBI would clear the mismatch but it doesn't solve the > temporary difference between sibling cores. I think the only guarantee > here is if CnP is turned on after the feature in question. > Thanks for explanation, I'll send updated version shortly! Cheers Vladimir _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel