[PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call

Pavel Tatashin
2019-11-21T18:48:13Z

privcmd_call requires to enable access to userspace for the
duration of the hypercall.

Currently, this is done via assembly macros. Change it to C
inlines instead.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
---
arch/arm/include/asm/assembler.h | 2 +-
arch/arm/include/asm/uaccess.h | 32 ++++++++++++++++++++++++++------
arch/arm/xen/enlighten.c | 2 +-
arch/arm/xen/hypercall.S | 15 ++-------------
arch/arm64/xen/hypercall.S | 19 ++-----------------
include/xen/arm/hypercall.h | 23 ++++++++++++++++++++---
6 files changed, 52 insertions(+), 41 deletions(-)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 99929122dad7..8e9262a0f016 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -480,7 +480,7 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
.macro uaccess_disable, tmp, isb=1
#ifdef CONFIG_CPU_SW_DOMAIN_PAN
/*
- * Whenever we re-enter userspace, the domains should always be
+ * Whenever we re-enter kernel, the domains should always be
* set appropriately.
*/
mov \tmp, #DACR_UACCESS_DISABLE
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 98c6b91be4a8..79d4efa3eb62 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -16,6 +16,23 @@

#include <asm/extable.h>

+#ifdef CONFIG_CPU_SW_DOMAIN_PAN
+static __always_inline void uaccess_enable(void)
+{
+ unsigned long val = DACR_UACCESS_ENABLE;
+
+ asm volatile("mcr p15, 0, %0, c3, c0, 0" : : "r" (val));
+ isb();
+}
+
+static __always_inline void uaccess_disable(void)
+{
+ unsigned long val = DACR_UACCESS_ENABLE;
+
+ asm volatile("mcr p15, 0, %0, c3, c0, 0" : : "r" (val));
+ isb();
+}
+
/*
* These two functions allow hooking accesses to userspace to increase
* system integrity by ensuring that the kernel can not inadvertantly
@@ -24,7 +41,6 @@
*/
static __always_inline unsigned int uaccess_save_and_enable(void)
{
-#ifdef CONFIG_CPU_SW_DOMAIN_PAN
unsigned int old_domain = get_domain();

/* Set the current domain access to permit user accesses */
@@ -32,18 +48,22 @@ static __always_inline unsigned int uaccess_save_and_enable(void)
domain_val(DOMAIN_USER, DOMAIN_CLIENT));

return old_domain;
-#else
- return 0;
-#endif
}

static __always_inline void uaccess_restore(unsigned int flags)
{
-#ifdef CONFIG_CPU_SW_DOMAIN_PAN
/* Restore the user access mask */
set_domain(flags);
-#endif
}
+#else
+static __always_inline void uaccess_enable(void) {}
+static __always_inline void uaccess_disable(void) {}
+static __always_inline unsigned int uaccess_save_and_enable(void)
+{
+ return 0;
+}
+static __always_inline void uaccess_restore(unsigned int flags) {}
+#endif /* CONFIG_CPU_SW_DOMAIN_PAN */

/*
* These two are intentionally not defined anywhere - if the kernel
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index dd6804a64f1a..e87280c6d25d 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -440,4 +440,4 @@ EXPORT_SYMBOL_GPL(HYPERVISOR_platform_op_raw);
EXPORT_SYMBOL_GPL(HYPERVISOR_multicall);
EXPORT_SYMBOL_GPL(HYPERVISOR_vm_assist);
EXPORT_SYMBOL_GPL(HYPERVISOR_dm_op);
-EXPORT_SYMBOL_GPL(privcmd_call);
+EXPORT_SYMBOL_GPL(arch_privcmd_call);
diff --git a/arch/arm/xen/hypercall.S b/arch/arm/xen/hypercall.S
index b11bba542fac..2f5be0dc6195 100644
--- a/arch/arm/xen/hypercall.S
+++ b/arch/arm/xen/hypercall.S
@@ -94,29 +94,18 @@ HYPERCALL2(multicall);
HYPERCALL2(vm_assist);
HYPERCALL3(dm_op);

-ENTRY(privcmd_call)
+ENTRY(arch_privcmd_call)
stmdb sp!, {r4}
mov r12, r0
mov r0, r1
mov r1, r2
mov r2, r3
ldr r3, [sp, #8]
- /*
- * Privcmd calls are issued by the userspace. We need to allow the
- * kernel to access the userspace memory before issuing the hypercall.
- */
- uaccess_enable r4

/* r4 is loaded now as we use it as scratch register before */
ldr r4, [sp, #4]
__HVC(XEN_IMM)

- /*
- * Disable userspace access from kernel. This is fine to do it
- * unconditionally as no set_fs(KERNEL_DS) is called before.
- */
- uaccess_disable r4
-
ldm sp!, {r4}
ret lr
-ENDPROC(privcmd_call);
+ENDPROC(arch_privcmd_call);
diff --git a/arch/arm64/xen/hypercall.S b/arch/arm64/xen/hypercall.S
index c5f05c4a4d00..921611778d2a 100644
--- a/arch/arm64/xen/hypercall.S
+++ b/arch/arm64/xen/hypercall.S
@@ -49,7 +49,6 @@

#include <linux/linkage.h>
#include <asm/assembler.h>
-#include <asm/asm-uaccess.h>
#include <xen/interface/xen.h>

@@ -86,27 +85,13 @@ HYPERCALL2(multicall);
HYPERCALL2(vm_assist);
HYPERCALL3(dm_op);

-ENTRY(privcmd_call)
+ENTRY(arch_privcmd_call)
mov x16, x0
mov x0, x1
mov x1, x2
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, x8
hvc XEN_IMM
-
- /*
- * Disable userspace access from kernel once the hyp call completed.
- */
- uaccess_ttbr0_disable x6, x7
ret
-ENDPROC(privcmd_call);
+ENDPROC(arch_privcmd_call);
diff --git a/include/xen/arm/hypercall.h b/include/xen/arm/hypercall.h
index b40485e54d80..cfb704fd78c8 100644
--- a/include/xen/arm/hypercall.h
+++ b/include/xen/arm/hypercall.h
@@ -34,16 +34,33 @@
#define _ASM_ARM_XEN_HYPERCALL_H

#include <linux/bug.h>
+#include <linux/uaccess.h>

#include <xen/interface/xen.h>
#include <xen/interface/sched.h>
#include <xen/interface/platform.h>

struct xen_dm_op_buf;
+long arch_privcmd_call(unsigned int call, unsigned long a1,
+ unsigned long a2, unsigned long a3,
+ unsigned long a4, unsigned long a5);

-long privcmd_call(unsigned call, unsigned long a1,
- unsigned long a2, unsigned long a3,
- unsigned long a4, unsigned long a5);
+static inline long privcmd_call(unsigned int call, unsigned long a1,
+ unsigned long a2, unsigned long a3,
+ unsigned long a4, unsigned long a5)
+{
+ long rv;
+
+ /*
+ * Privcmd calls are issued by the userspace. We need to allow the
+ * kernel to access the userspace memory before issuing the hypercall.
+ */
+ uaccess_enable();
+ rv = arch_privcmd_call(call, a1, a2, a3, a4, a5);
+ uaccess_disable();
+
+ return rv;
+}
int HYPERVISOR_xen_version(int cmd, void *arg);
int HYPERVISOR_console_io(int cmd, int count, char *str);
int HYPERVISOR_grant_table_op(unsigned int cmd, void *uop, unsigned int count);
--
2.24.0