From: Mark Rutland mark.rutland@arm.com
[ Upstream commit ca1314d73eed493c49bb1932c60a8605530db2e4 ]
In el0_svc_common() we unmask exceptions before we call user_exit(), and so there's a window where an IRQ or debug exception can be taken while RCU is not watching. In do_debug_exception() we account for this in via debug_exception_{enter,exit}(), but in the el1_irq asm we do not and we call trace functions which rely on RCU before we have a guarantee that RCU is watching.
Let's avoid this by having el0_svc_common() exit userspace before unmasking exceptions, matching what we do for all other EL0 entry paths. We can use user_exit_irqoff() to avoid the pointless save/restore of IRQ flags while we're sure exceptions are masked in DAIF.
The workaround for Cortex-A76 erratum 1463225 may trigger a debug exception before this point, but the debug code invoked in this case is safe even when RCU is not watching.
Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: James Morse james.morse@arm.com Cc: Will Deacon will@kernel.org Link: https://lore.kernel.org/r/20201130115950.22492-2-mark.rutland@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/syscall.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index 1457a0ba83dbc..f2d2dbbbfca20 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -102,8 +102,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, regs->syscallno = scno;
cortex_a76_erratum_1463225_svc_handler(); + user_exit_irqoff(); local_daif_restore(DAIF_PROCCTX); - user_exit();
if (has_syscall_work(flags)) { /* set default errno for user-issued syscall(-1) */