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Thu, 01 Oct 2020 16:11:47 -0700 (PDT) Date: Fri, 2 Oct 2020 01:10:27 +0200 In-Reply-To: Message-Id: <1466ded7cb14ef17258b12a17129d2ca62f81911.1601593784.git.andreyknvl@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.28.0.709.gb0816b6eb0-goog Subject: [PATCH v4 26/39] arm64: mte: Add in-kernel tag fault handler From: Andrey Konovalov To: Dmitry Vyukov , Vincenzo Frascino , Catalin Marinas , kasan-dev@googlegroups.com Cc: Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Vincenzo Frascino Add the implementation of the in-kernel fault handler. When a tag fault happens on a kernel address: * MTE is disabled on the current CPU, * the execution continues. When a tag fault happens on a user address: * the kernel executes do_bad_area() and panics. The tag fault handler for kernel addresses is currently empty and will be filled in by a future commit. Signed-off-by: Vincenzo Frascino Co-developed-by: Andrey Konovalov Signed-off-by: Andrey Konovalov Reviewed-by: Catalin Marinas --- Change-Id: I9b8aa79567f7c45f4d6a1290efcf34567e620717 --- arch/arm64/include/asm/uaccess.h | 23 +++++++++++++++++++ arch/arm64/mm/fault.c | 38 +++++++++++++++++++++++++++++++- 2 files changed, 60 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index 991dd5f031e4..c7fff8daf2a7 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -200,13 +200,36 @@ do { \ CONFIG_ARM64_PAN)); \ } while (0) +/* + * The Tag Check Flag (TCF) mode for MTE is per EL, hence TCF0 + * affects EL0 and TCF affects EL1 irrespective of which TTBR is + * used. + * The kernel accesses TTBR0 usually with LDTR/STTR instructions + * when UAO is available, so these would act as EL0 accesses using + * TCF0. + * However futex.h code uses exclusives which would be executed as + * EL1, this can potentially cause a tag check fault even if the + * user disables TCF0. + * + * To address the problem we set the PSTATE.TCO bit in uaccess_enable() + * and reset it in uaccess_disable(). + * + * The Tag check override (TCO) bit disables temporarily the tag checking + * preventing the issue. + */ static inline void uaccess_disable(void) { + asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(0), + ARM64_MTE, CONFIG_KASAN_HW_TAGS)); + __uaccess_disable(ARM64_HAS_PAN); } static inline void uaccess_enable(void) { + asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(1), + ARM64_MTE, CONFIG_KASAN_HW_TAGS)); + __uaccess_enable(ARM64_HAS_PAN); } diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index a3bd189602df..d110f382dacf 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -33,6 +33,7 @@ #include #include #include +#include #include #include #include @@ -294,6 +295,11 @@ static void die_kernel_fault(const char *msg, unsigned long addr, do_exit(SIGKILL); } +static void report_tag_fault(unsigned long addr, unsigned int esr, + struct pt_regs *regs) +{ +} + static void __do_kernel_fault(unsigned long addr, unsigned int esr, struct pt_regs *regs) { @@ -641,10 +647,40 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) return 0; } +static void do_tag_recovery(unsigned long addr, unsigned int esr, + struct pt_regs *regs) +{ + static bool reported = false; + + if (!READ_ONCE(reported)) { + report_tag_fault(addr, esr, regs); + WRITE_ONCE(reported, true); + } + + /* + * Disable MTE Tag Checking on the local CPU for the current EL. + * It will be done lazily on the other CPUs when they will hit a + * tag fault. + */ + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_NONE); + isb(); +} + + static int do_tag_check_fault(unsigned long addr, unsigned int esr, struct pt_regs *regs) { - do_bad_area(addr, esr, regs); + /* + * The tag check fault (TCF) is per EL, hence TCF0 affects + * EL0 and TCF affects EL1. + * TTBR0 address belong by convention to EL0 hence to correctly + * discriminate we use the is_ttbr0_addr() macro. + */ + if (is_ttbr0_addr(addr)) + do_bad_area(addr, esr, regs); + else + do_tag_recovery(addr, esr, regs); + return 0; }