arm64: entry: Apply BP hardening for suspicious interrupts from EL0

From: Will Deacon <will.deacon@arm.com>

commit 30d88c0e3ace625a92eead9ca0ad94093a8f59fe upstream.

It is possible to take an IRQ from EL0 following a branch to a kernel
address in such a way that the IRQ is prioritised over the instruction
abort. Whilst an attacker would need to get the stars to align here,
it might be sufficient with enough calibration so perform BP hardening
in the rare case that we see a kernel address in the ELR when handling
an IRQ from EL0.

Reported-by: Dan Hettena <dhettena@nvidia.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 30f4331d477a7d3475f1f56b44fa9dc91ae0ec1f..b79e302d2a3e959af52a886a8bff821327259d88 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -686,6 +686,11 @@ el0_irq_naked:
 #endif
 
        ct_user_exit
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+       tbz     x22, #55, 1f
+       bl      do_el0_irq_bp_hardening
+1:
+#endif
        irq_handler
 
 #ifdef CONFIG_TRACE_IRQFLAGS

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 6120a148605415278650d5bef46357f416b7728b..ad49ae8f3967b442ee8d1be292cc34f93f1e3665 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -590,6 +590,12 @@ asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
        arm64_notify_die("", regs, &info, esr);
 }
 
+asmlinkage void __exception do_el0_irq_bp_hardening(void)
+{
+       /* PC has already been checked in entry.S */
+       arm64_apply_bp_hardening();
+}
+
 asmlinkage void __exception do_el0_ia_bp_hardening(unsigned long addr,
                                                   unsigned int esr,
                                                   struct pt_regs *regs)