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so3: terminate the faulting user process on an EL0 abort instead of panicking #301

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so3: terminate the faulting user process on an EL0 abort instead of panicking #301

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44 changes: 42 additions & 2 deletions so3/so3/arch/arm64/traps.c
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,9 @@

#else /* CONFIG_AVZ */
#include <syscall.h>
#include <process.h>
#include <schedule.h>
#include <signal.h>
#endif /* !CONFIG_AVZ */

#include <asm/processor.h>
Expand Down Expand Up @@ -215,9 +218,36 @@ int dabt_handle(cpu_regs_t *regs, unsigned long esr)
#endif
}

#ifndef CONFIG_AVZ
/* A synchronous abort taken from a lower EL (EL0) is a fault in the running
* user process — typically a NULL-pointer dereference. Report which process
* faulted and where, then terminate that process ONLY, so the shell regains
* control instead of the whole kernel panicking. Kernel-mode (EL1) faults use a
* different exception class (DABT/IABT "current EL") and still reach the fatal
* path in trap_handle(). */

static void user_fault(unsigned long esr)
{
unsigned long far = read_sysreg(far_el1);
unsigned long elr = read_sysreg(elr_el1);
pcb_t *pcb = current()->pcb;

printk("[SO3] process \"%s\" (pid %d) faulted at address 0x%lx (pc=0x%lx, ESR=0x%lx) - terminating it.\n",
pcb ? pcb->name : "?", pcb ? pcb->pid : -1, far, elr, esr);

/* Terminate the offending process. sys_do_exit_group() sets it zombie and
* schedules away, so it does not return here; the parent's wait4() reaps
* it and the shell reprints its prompt. IRQs must be enabled for the
* scheduler, as in the syscall path above. */

local_irq_enable();
sys_do_exit_group(128 + SIGSEGV);
}
#endif /* !CONFIG_AVZ */

/**
* This is the entry point for all exceptions currently managed by SO3.
*
*
* Regarding the SOO hypercalls, all addresses got from arguments
* *must* be physical addresses.
*
Expand Down Expand Up @@ -253,8 +283,13 @@ void trap_handle(cpu_regs_t *regs)
case ESR_ELx_EC_DABT_LOW:

ret = dabt_handle(regs, esr);
if (ret == -1)
if (ret == -1) {
#ifdef CONFIG_AVZ
goto __err;
#else
user_fault(esr); /* EL0 data abort: terminate the user process */
#endif
}
break;

/* SVC used for syscalls */
Expand Down Expand Up @@ -429,7 +464,12 @@ void trap_handle(cpu_regs_t *regs)
}

case ESR_ELx_EC_IABT_LOW:
#ifdef CONFIG_AVZ
goto __err;
#else
user_fault(esr); /* EL0 instruction abort: terminate the user process */
break;
#endif

default:
__err:
Expand Down
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