Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752391AbdLFOda (ORCPT ); Wed, 6 Dec 2017 09:33:30 -0500 Received: from foss.arm.com ([217.140.101.70]:36504 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752612AbdLFOcv (ORCPT ); Wed, 6 Dec 2017 09:32:51 -0500 Date: Wed, 6 Dec 2017 14:32:43 +0000 From: Mark Rutland To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, ard.biesheuvel@linaro.org, sboyd@codeaurora.org, dave.hansen@linux.intel.com, keescook@chromium.org, msalter@redhat.com, labbott@redhat.com, tglx@linutronix.de Subject: Re: [PATCH v3 11/20] arm64: mm: Map entry trampoline into trampoline and kernel page tables Message-ID: <20171206143243.rzcssrrkomyb66jg@lakrids.cambridge.arm.com> References: <1512563739-25239-1-git-send-email-will.deacon@arm.com> <1512563739-25239-12-git-send-email-will.deacon@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1512563739-25239-12-git-send-email-will.deacon@arm.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4144 Lines: 115 On Wed, Dec 06, 2017 at 12:35:30PM +0000, Will Deacon wrote: > The exception entry trampoline needs to be mapped at the same virtual > address in both the trampoline page table (which maps nothing else) > and also the kernel page table, so that we can swizzle TTBR1_EL1 on > exceptions from and return to EL0. > > This patch maps the trampoline at a fixed virtual address in the fixmap > area of the kernel virtual address space, which allows the kernel proper > to be randomized with respect to the trampoline when KASLR is enabled. > > Signed-off-by: Will Deacon Reviewed-by: Mark Rutland Mark. > --- > arch/arm64/include/asm/fixmap.h | 4 ++++ > arch/arm64/include/asm/pgtable.h | 1 + > arch/arm64/kernel/asm-offsets.c | 6 +++++- > arch/arm64/mm/mmu.c | 23 +++++++++++++++++++++++ > 4 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h > index 4052ec39e8db..8119b49be98d 100644 > --- a/arch/arm64/include/asm/fixmap.h > +++ b/arch/arm64/include/asm/fixmap.h > @@ -58,6 +58,10 @@ enum fixed_addresses { > FIX_APEI_GHES_NMI, > #endif /* CONFIG_ACPI_APEI_GHES */ > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > + FIX_ENTRY_TRAMP_TEXT, > +#define TRAMP_VALIAS (__fix_to_virt(FIX_ENTRY_TRAMP_TEXT)) > +#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ > __end_of_permanent_fixed_addresses, > > /* > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 149d05fb9421..774003b247ad 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -680,6 +680,7 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm, > > extern pgd_t swapper_pg_dir[PTRS_PER_PGD]; > extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; > +extern pgd_t tramp_pg_dir[PTRS_PER_PGD]; > > /* > * Encode and decode a swap entry: > diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c > index 71bf088f1e4b..af247d10252f 100644 > --- a/arch/arm64/kernel/asm-offsets.c > +++ b/arch/arm64/kernel/asm-offsets.c > @@ -24,6 +24,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -148,11 +149,14 @@ int main(void) > DEFINE(ARM_SMCCC_RES_X2_OFFS, offsetof(struct arm_smccc_res, a2)); > DEFINE(ARM_SMCCC_QUIRK_ID_OFFS, offsetof(struct arm_smccc_quirk, id)); > DEFINE(ARM_SMCCC_QUIRK_STATE_OFFS, offsetof(struct arm_smccc_quirk, state)); > - > BLANK(); > DEFINE(HIBERN_PBE_ORIG, offsetof(struct pbe, orig_address)); > DEFINE(HIBERN_PBE_ADDR, offsetof(struct pbe, address)); > DEFINE(HIBERN_PBE_NEXT, offsetof(struct pbe, next)); > DEFINE(ARM64_FTR_SYSVAL, offsetof(struct arm64_ftr_reg, sys_val)); > + BLANK(); > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > + DEFINE(TRAMP_VALIAS, TRAMP_VALIAS); > +#endif > return 0; > } > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 267d2b79d52d..fe68a48c64cb 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -525,6 +525,29 @@ static int __init parse_rodata(char *arg) > } > early_param("rodata", parse_rodata); > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > +static int __init map_entry_trampoline(void) > +{ > + extern char __entry_tramp_text_start[]; > + > + pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC; > + phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start); > + > + /* The trampoline is always mapped and can therefore be global */ > + pgprot_val(prot) &= ~PTE_NG; > + > + /* Map only the text into the trampoline page table */ > + memset(tramp_pg_dir, 0, PGD_SIZE); > + __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE, > + prot, pgd_pgtable_alloc, 0); > + > + /* ...as well as the kernel page table */ > + __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot); > + return 0; > +} > +core_initcall(map_entry_trampoline); > +#endif > + > /* > * Create fine-grained mappings for the kernel. > */ > -- > 2.1.4 >