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arm64: avoid returning from bad_mode 

Generally, taking an unexpected exception should be a fatal event, and
bad_mode is intended to cater for this. However, it should be possible
to contain unexpected synchronous exceptions from EL0 without bringing
the kernel down, by sending a SIGILL to the task.

We tried to apply this approach in commit 9955ac47f4 ("arm64:
don't kill the kernel on a bad esr from el0"), by sending a signal for
any bad_mode call resulting from an EL0 exception.

However, this also applies to other unexpected exceptions, such as
SError and FIQ. The entry paths for these exceptions branch to bad_mode
without configuring the link register, and have no kernel_exit. Thus, if
we take one of these exceptions from EL0, bad_mode will eventually
return to the original user link register value.

This patch fixes this by introducing a new bad_el0_sync handler to cater
for the recoverable case, and restoring bad_mode to its original state,
whereby it calls panic() and never returns. The recoverable case
branches to bad_el0_sync with a bl, and returns to userspace via the
usual ret_to_user mechanism.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 9955ac47f4 ("arm64: don't kill the kernel on a bad esr from el0")
Reported-by: Mark Salter <msalter@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Mark Rutland 2017-01-18 17:23:41 +00:00 committed by Catalin Marinas
parent ad9e202aa1
commit 7d9e8f71b9
2 changed files with 25 additions and 5 deletions
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2
arch/arm64/kernel/entry.S
View File

@ -683,7 +683,7 @@ el0_inv:
mov x0, sp
mov x1, #BAD_SYNC
mov x2, x25
bl bad_mode
bl bad_el0_sync
b ret_to_user
ENDPROC(el0_sync)

28
arch/arm64/kernel/traps.c
View File

@ -604,17 +604,34 @@ const char *esr_get_class_string(u32 esr)
}
/*
* bad_mode handles the impossible case in the exception vector.
* bad_mode handles the impossible case in the exception vector. This is always
* fatal.
*/
asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr)
{
siginfo_t info;
void __user *pc = (void __user *)instruction_pointer(regs);
console_verbose();
pr_crit("Bad mode in %s handler detected on CPU%d, code 0x%08x -- %s\n",
handler[reason], smp_processor_id(), esr,
esr_get_class_string(esr));
die("Oops - bad mode", regs, 0);
local_irq_disable();
panic("bad mode");
}
/*
* bad_el0_sync handles unexpected, but potentially recoverable synchronous
* exceptions taken from EL0. Unlike bad_mode, this returns.
*/
asmlinkage void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr)
{
siginfo_t info;
void __user *pc = (void __user *)instruction_pointer(regs);
console_verbose();
pr_crit("Bad EL0 synchronous exception detected on CPU%d, code 0x%08x -- %s\n",
smp_processor_id(), esr, esr_get_class_string(esr));
__show_regs(regs);
info.si_signo = SIGILL;
@ -622,7 +639,10 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr)
info.si_code = ILL_ILLOPC;
info.si_addr = pc;
arm64_notify_die("Oops - bad mode", regs, &info, 0);
current->thread.fault_address = 0;
current->thread.fault_code = 0;
force_sig_info(info.si_signo, &info, current);
}
void __pte_error(const char *file, int line, unsigned long val)