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

[Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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


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