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UPSTREAM: arm64: xen: Enable user access before a privcmd hvc call

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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@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 31432001
Change-Id: I64d827923d869c1868702c8a18efa99ea91d3151
(cherry picked from commit 9cf09d68b89ae5fe0261dcc69464bcc676900af6)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Catalin Marinas 2016-07-05 12:25:15 +01:00 • committed by Amit Pundir
parent 23df43f5fc
commit 62a7c6fac9
1 changed files with 15 additions and 0 deletions
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15
arch/arm64/xen/hypercall.S
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@ -49,6 +49,7 @@
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/uaccess.h>
#include <xen/interface/xen.h>
@ -89,6 +90,20 @@ 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);