On Fri, Aug 14, 2020 at 07:27:03PM +0200, Andrey Konovalov wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 5e832b3387f1..c62c8ba85c0e 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -33,6 +33,7 @@
> #include <asm/debug-monitors.h>
> #include <asm/esr.h>
> #include <asm/kprobes.h>
> +#include <asm/mte.h>
> #include <asm/processor.h>
> #include <asm/sysreg.h>
> #include <asm/system_misc.h>
> @@ -222,6 +223,20 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
> return 1;
> }
>
> +static bool is_el1_mte_sync_tag_check_fault(unsigned int esr)
> +{
> + unsigned int ec = ESR_ELx_EC(esr);
> + unsigned int fsc = esr & ESR_ELx_FSC;
> +
> + if (ec != ESR_ELx_EC_DABT_CUR)
> + return false;
> +
> + if (fsc == ESR_ELx_FSC_MTE)
> + return true;
> +
> + return false;
> +}
> +
> static bool is_el1_instruction_abort(unsigned int esr)
> {
> return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_CUR;
> @@ -294,6 +309,18 @@ 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)
> +{
> + bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> +
> + pr_alert("Memory Tagging Extension Fault in %pS\n", (void *)regs->pc);
> + pr_alert(" %s at address %lx\n", is_write ? "Write" : "Read", addr);
> + pr_alert(" Pointer tag: [%02x], memory tag: [%02x]\n",
> + mte_get_ptr_tag(addr),
> + mte_get_mem_tag((void *)addr));
> +}
> +
> static void __do_kernel_fault(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> {
> @@ -317,12 +344,16 @@ static void __do_kernel_fault(unsigned long addr,
> unsigned int esr,
> msg = "execute from non-executable memory";
> else
> msg = "read from unreadable memory";
> + } else if (is_el1_mte_sync_tag_check_fault(esr)) {
> + report_tag_fault(addr, esr, regs);
> + msg = "memory tagging extension fault";
IIUC, that's dead code. See my comment below on do_tag_check_fault().
> } else if (addr < PAGE_SIZE) {
> msg = "NULL pointer dereference";
> } else {
> msg = "paging request";
> }
>
> +
Unnecessary empty line.
> die_kernel_fault(msg, addr, esr, regs);
> }
>
> @@ -658,10 +689,27 @@ static int do_sea(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> return 0;
> }
>
> +static int do_tag_recovery(unsigned long addr, unsigned int esr,
> + struct pt_regs *regs)
> +{
> + report_tag_fault(addr, esr, regs);
> +
> + /* Skip over the faulting instruction and continue: */
> + arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
Ooooh, do we expect the kernel to still behave correctly after this? I
thought the recovery means disabling tag checking altogether and
restarting the instruction rather than skipping over it. We only skip if
we emulated it.
> +
> + return 0;
> +}
> +
> +
> 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 TTBR */
> + if (is_ttbr0_addr(addr))
> + do_bad_area(addr, esr, regs);
> + else
> + do_tag_recovery(addr, esr, regs);
So we never invoke __do_kernel_fault() for a synchronous tag check in
the kernel. What's with all the is_el1_mte_sync_tag_check_fault() check
above?
--
Catalin
