[PATCH v3 6/7] arm64: xen: Enable user access before a privcmd hvc call
From: catalin.marinas@arm.com (Catalin Marinas)
Date: 2016-09-13 17:46:36
Subsystem:
arm64 port (aarch64 architecture), the rest, xen hypervisor arm64 · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds, Stefano Stabellini
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 <redacted> Acked-by: Stefano Stabellini <sstabellini@kernel.org> Cc: Will Deacon <redacted> Cc: James Morse <james.morse@arm.com> Cc: Kees Cook <redacted> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> --- arch/arm64/xen/hypercall.S | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/arch/arm64/xen/hypercall.S b/arch/arm64/xen/hypercall.S
index 329c8027b0a9..a23b2e8f2647 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 +92,24 @@ ENTRY(privcmd_call) mov x2, x3 mov x3, x4 mov x4, x5 +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + /* + * 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_enable_not_uao x6, x7 +#endif hvc XEN_IMM + +#ifdef CONFIG_ARM64_SW_TTBR0_PAN + /* + * Disable userspace access from kernel once the hyp call completed. + */ + uaccess_disable_not_uao x6 +#endif ret ENDPROC(privcmd_call);