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Message-Id: <1477675636-3957-8-git-send-email-catalin.marinas@arm.com>
Date: Fri, 28 Oct 2016 18:27:15 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Will Deacon <will.deacon@....com>,
James Morse <james.morse@....com>,
Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
AKASHI Takahiro <takahiro.akashi@...aro.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v4 7/8] arm64: xen: Enable user access before a privcmd hvc call
Privcmd calls are issued by the userspace. The kernel needs to enable
access to TTBR0_EL1 as the hypervisor would issue stage 1 translations
to user memory via AT instructions. Since AT instructions are not
affected by the PAN bit (ARMv8.1), we only need the explicit
uaccess_enable/disable if the TTBR0 PAN option is enabled.
Reviewed-by: Julien Grall <julien.grall@....com>
Acked-by: Stefano Stabellini <sstabellini@...nel.org>
Cc: Will Deacon <will.deacon@....com>
Cc: James Morse <james.morse@....com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
arch/arm64/xen/hypercall.S | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/arm64/xen/hypercall.S b/arch/arm64/xen/hypercall.S
index 329c8027b0a9..b41aff25426d 100644
--- a/arch/arm64/xen/hypercall.S
+++ b/arch/arm64/xen/hypercall.S
@@ -49,6 +49,7 @@
#include <linux/linkage.h>
#include <asm/assembler.h>
+#include <asm/uaccess.h>
#include <xen/interface/xen.h>
@@ -91,6 +92,20 @@ ENTRY(privcmd_call)
mov x2, x3
mov x3, x4
mov x4, x5
+ /*
+ * Privcmd calls are issued by the userspace. The kernel needs to
+ * enable access to TTBR0_EL1 as the hypervisor would issue stage 1
+ * translations to user memory via AT instructions. Since AT
+ * instructions are not affected by the PAN bit (ARMv8.1), we only
+ * need the explicit uaccess_enable/disable if the TTBR0 PAN emulation
+ * is enabled (it implies that hardware UAO and PAN disabled).
+ */
+ uaccess_ttbr0_enable x6, x7
hvc XEN_IMM
+
+ /*
+ * Disable userspace access from kernel once the hyp call completed.
+ */
+ uaccess_ttbr0_disable x6
ret
ENDPROC(privcmd_call);
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