On 8/27/20 10:54 AM, Catalin Marinas wrote:
> 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().
>
That's correct. This was useful with "panic_on_mte_fault" kernel command line
parameter. Since it has now been replaced by a similar kasan feature, this code
can be safely removed.
>> } else if (addr < PAGE_SIZE) {
>> msg = "NULL pointer dereference";
>> } else {
>> msg = "paging request";
>> }
>>
>> +
>
> Unnecessary empty line.
>
Agree.
>> 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.
>
I tried to dig it out but I am not sure why we need this as well.
>> +
>> + 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?
>
That's correct. This had a meaning with "panic_on_mte_fault" but since the
feature has been replaced is_el1_mte_sync_tag_check_fault() is not useful
anymore.
--
Regards,
Vincenzo
