[PATCH] arm/arm64: KVM: Map the BSS at HYP

[PATCH] arm/arm64: KVM: Map the BSS at HYP

[Marc Zyngier]

When used with a compiler that doesn't implement "asm goto"
(such as the AArch64 port of GCC 4.8), jump labels generate a
memory access to find out about the value of the key (instead
of just patching the code). The key itself is likely to be
stored in the BSS.

This is perfectly fine, except that we don't map the BSS at HYP,
leading to an exploding kernel at the first access. The obvious
fix is simply to map the BSS there (which should have been done
a long while ago, but hey...).

Reported-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/arm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 09942f0..14adf40 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -1345,6 +1345,13 @@ static int init_hyp_mode(void)
 		goto out_err;
 	}
 
+	err = create_hyp_mappings(kvm_ksym_ref(__bss_start),
+				  kvm_ksym_ref(__bss_stop), PAGE_HYP_RO);
+	if (err) {
+		kvm_err("Cannot map bss section\n");
+		goto out_err;
+	}
+
 	/*
 	 * Map the Hyp stack pages
 	 */
-- 
2.1.4

[PATCH] arm/arm64: KVM: Map the BSS at HYP

[Christoffer Dall]

On Thu, Oct 20, 2016 at 02:00:41PM +0100, Marc Zyngier wrote:
> When used with a compiler that doesn't implement "asm goto"
> (such as the AArch64 port of GCC 4.8), jump labels generate a
> memory access to find out about the value of the key (instead
> of just patching the code). The key itself is likely to be
> stored in the BSS.
> 
> This is perfectly fine, except that we don't map the BSS at HYP,
> leading to an exploding kernel at the first access. The obvious
> fix is simply to map the BSS there (which should have been done
> a long while ago, but hey...).
> 
> Reported-by: Eric Auger <eric.auger@redhat.com>
> Tested-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>