On 06/22/2015 08:12 AM, Will Deacon wrote:
I still think we should be disabling userspace access to the DCC if the
kernel is using it as its console.
I still need help with this. I know you said a year ago that
MDSCR_EL1.TDCC needs to be set to disable userspace access. Where and
how should I do this? I can do this:
static int __init hvc_dcc_console_init(void)
{
#ifdef CONFIG_ARM64
u32 val;
asm("msr mdscr_el1, %0 "
"orr %0, %0, #4096 " /* TDCC */
"msr %0, mdscr_el1 "
: "=r" (val));
#endif
But this seems clunky.
I am concerned about KVM, though. There appears to be code in KVM in
hyp.s and sys_regs.c that touches and/or emulates MDSCR_EL1.
On a side note, it does not appear that ARM32 blocks userspace DCC. I
don't see where DBGDSCR.UDCCdis is set.
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