From 34bfeea4a9e9cdae713637541f240c3adfdfede3 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Mon, 4 May 2020 14:42:36 +0100 Subject: arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Pages allocated by the kernel are not guaranteed to have the tags zeroed, especially as the kernel does not (yet) use MTE itself. To ensure the user can still access such pages when mapped into its address space, clear the tags via set_pte_at(). A new page flag - PG_mte_tagged (PG_arch_2) - is used to track pages with valid allocation tags. Since the zero page is mapped as pte_special(), it won't be covered by the above set_pte_at() mechanism. Clear its tags during early MTE initialisation. Co-developed-by: Steven Price Signed-off-by: Steven Price Signed-off-by: Catalin Marinas Cc: Will Deacon --- arch/arm64/lib/Makefile | 2 ++ arch/arm64/lib/mte.S | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 36 insertions(+) create mode 100644 arch/arm64/lib/mte.S (limited to 'arch/arm64/lib') diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile index 2fc253466dbf..d31e1169d9b8 100644 --- a/arch/arm64/lib/Makefile +++ b/arch/arm64/lib/Makefile @@ -16,3 +16,5 @@ lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o obj-$(CONFIG_CRC32) += crc32.o obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o + +obj-$(CONFIG_ARM64_MTE) += mte.o diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S new file mode 100644 index 000000000000..a36705640086 --- /dev/null +++ b/arch/arm64/lib/mte.S @@ -0,0 +1,34 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2020 ARM Ltd. + */ +#include + +#include +#include + + .arch armv8.5-a+memtag + +/* + * multitag_transfer_size - set \reg to the block size that is accessed by the + * LDGM/STGM instructions. + */ + .macro multitag_transfer_size, reg, tmp + mrs_s \reg, SYS_GMID_EL1 + ubfx \reg, \reg, #SYS_GMID_EL1_BS_SHIFT, #SYS_GMID_EL1_BS_SIZE + mov \tmp, #4 + lsl \reg, \tmp, \reg + .endm + +/* + * Clear the tags in a page + * x0 - address of the page to be cleared + */ +SYM_FUNC_START(mte_clear_page_tags) + multitag_transfer_size x1, x2 +1: stgm xzr, [x0] + add x0, x0, x1 + tst x0, #(PAGE_SIZE - 1) + b.ne 1b + ret +SYM_FUNC_END(mte_clear_page_tags) -- cgit v1.2.3