[PATCHv3 12/17] arm64: uaccess: split user/kernel routines

Mark Rutland
2020-10-26T13:38:01Z

This patch separates arm64's user and kernel memory access primitives
into distinct routines, adding new __{get,put}_kernel_nofault() helpers
to acess kernel memory, upon which core code builds larger copy
routines.

The kernel access routines (using LDR/STR) are not affected by PAN (when
legitimately accessing kernel memory), nor are they affected by UAO.
Switching to KERNEL_DS may set UAO, but this does not adversely affect
the kernel access routines.

The user access routines (using LDTR/STTR) are not affected by PAN (when
legitimately accessing user memory), but are affected by UAO. As these
are only legitimate to use under USER_DS with UAO clear, this should not
be problematic.

Routines performing atomics to user memory (futex and deprecated
instruction emulation) still need to transiently clear PAN, and these
are left as-is. These are never used on kernel memory.

Subsequent patches will refactor the uaccess helpers to remove redundant
code, and will also remove the redundant PAN/UAO manipulation.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/asm-uaccess.h | 48 +++++----------------------
arch/arm64/include/asm/uaccess.h | 64 +++++++++++++++++++++---------------
2 files changed, 47 insertions(+), 65 deletions(-)

diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index 479222ab82d44..046196f08988b 100644
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h
@@ -59,62 +59,32 @@ alternative_else_nop_endif
#endif

/*
- * Generate the assembly for UAO alternatives with exception table entries.
+ * Generate the assembly for LDTR/STTR with exception table entries.
* This is complicated as there is no post-increment or pair versions of the
* unprivileged instructions, and USER() only works for single instructions.
*/
-#ifdef CONFIG_ARM64_UAO
.macro uao_ldp l, reg1, reg2, addr, post_inc
- alternative_if_not ARM64_HAS_UAO
-8888: ldp \reg1, \reg2, [\addr], \post_inc;
-8889: nop;
- nop;
- alternative_else
- ldtr \reg1, [\addr];
- ldtr \reg2, [\addr, #8];
- add \addr, \addr, \post_inc;
- alternative_endif
+8888: ldtr \reg1, [\addr];
+8889: ldtr \reg2, [\addr, #8];
+ add \addr, \addr, \post_inc;

_asm_extable 8888b,\l;
_asm_extable 8889b,\l;
.endm

.macro uao_stp l, reg1, reg2, addr, post_inc
- alternative_if_not ARM64_HAS_UAO
-8888: stp \reg1, \reg2, [\addr], \post_inc;
-8889: nop;
- nop;
- alternative_else
- sttr \reg1, [\addr];
- sttr \reg2, [\addr, #8];
- add \addr, \addr, \post_inc;
- alternative_endif
+8888: sttr \reg1, [\addr];
+8889: sttr \reg2, [\addr, #8];
+ add \addr, \addr, \post_inc;

_asm_extable 8888b,\l;
_asm_extable 8889b,\l;
.endm

.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
- alternative_if_not ARM64_HAS_UAO
-8888: \inst \reg, [\addr], \post_inc;
- nop;
- alternative_else
- \alt_inst \reg, [\addr];
- add \addr, \addr, \post_inc;
- alternative_endif
+8888: \alt_inst \reg, [\addr];
+ add \addr, \addr, \post_inc;

_asm_extable 8888b,\l;
.endm
-#else
- .macro uao_ldp l, reg1, reg2, addr, post_inc
- USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
- .endm
- .macro uao_stp l, reg1, reg2, addr, post_inc
- USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
- .endm
- .macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
- USER(\l, \inst \reg, [\addr], \post_inc)
- .endm
-#endif
-
#endif
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 4ad2990241d78..bc7f3ff24ccd5 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -24,6 +24,8 @@
#include <asm/memory.h>
#include <asm/extable.h>

+#define HAVE_GET_KERNEL_NOFAULT
+
#define get_fs() (current_thread_info()->addr_limit)

static inline void set_fs(mm_segment_t fs)
@@ -253,10 +255,9 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
* The "__xxx_error" versions set the third argument to -EFAULT if an error
* occurs, and leave it unchanged on success.
*/
-#define __get_mem_asm(instr, alt_instr, reg, x, addr, err, feature) \
+#define __get_mem_asm(ldr, reg, x, addr, err) \
asm volatile( \
- "1:"ALTERNATIVE(instr " " reg "1, [%2]\n", \
- alt_instr " " reg "1, [%2]\n", feature) \
+ "1: " ldr " " reg "1, [%2]\n" \
"2:\n" \
" .section .fixup, \"ax\"\n" \
" .align 2\n" \
@@ -268,26 +269,22 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
: "+r" (err), "=&r" (x) \
: "r" (addr), "i" (-EFAULT))

-#define __raw_get_mem(x, ptr, err) \
+#define __raw_get_mem(ldr, x, ptr, err) \
do { \
unsigned long __gu_val; \
__chk_user_ptr(ptr); \
switch (sizeof(*(ptr))) { \
case 1: \
- __get_mem_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __get_mem_asm(ldr "b", "%w", __gu_val, (ptr), (err)); \
break; \
case 2: \
- __get_mem_asm("ldrh", "ldtrh", "%w", __gu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __get_mem_asm(ldr "h", "%w", __gu_val, (ptr), (err)); \
break; \
case 4: \
- __get_mem_asm("ldr", "ldtr", "%w", __gu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __get_mem_asm(ldr, "%w", __gu_val, (ptr), (err)); \
break; \
case 8: \
- __get_mem_asm("ldr", "ldtr", "%x", __gu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __get_mem_asm(ldr, "%x", __gu_val, (ptr), (err)); \
break; \
default: \
BUILD_BUG(); \
@@ -298,7 +295,7 @@ do { \
#define __raw_get_user(x, ptr, err) \
do { \
uaccess_enable_not_uao(); \
- __raw_get_mem(x, ptr, err); \
+ __raw_get_mem("ldtr", x, ptr, err); \
uaccess_disable_not_uao(); \
} while (0)

@@ -323,10 +320,19 @@ do { \

#define get_user __get_user

-#define __put_mem_asm(instr, alt_instr, reg, x, addr, err, feature) \
+#define __get_kernel_nofault(dst, src, type, err_label) \
+do { \
+ int __gkn_err; \
+ \
+ __raw_get_mem("ldr", *((type *)(dst)), \
+ (__force type __user *)(src), __gkn_err); \
+ if (unlikely(__gkn_err)) \
+ goto err_label; \
+} while(0)
+
+#define __put_mem_asm(str, reg, x, addr, err) \
asm volatile( \
- "1:"ALTERNATIVE(instr " " reg "1, [%2]\n", \
- alt_instr " " reg "1, [%2]\n", feature) \
+ "1: " str " " reg "1, [%2]\n" \
"2:\n" \
" .section .fixup,\"ax\"\n" \
" .align 2\n" \
@@ -337,26 +343,22 @@ do { \
: "+r" (err) \
: "r" (x), "r" (addr), "i" (-EFAULT))

-#define __raw_put_mem(x, ptr, err) \
+#define __raw_put_mem(str, x, ptr, err) \
do { \
__typeof__(*(ptr)) __pu_val = (x); \
__chk_user_ptr(ptr); \
switch (sizeof(*(ptr))) { \
case 1: \
- __put_mem_asm("strb", "sttrb", "%w", __pu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __put_mem_asm(str "b", "%w", __pu_val, (ptr), (err)); \
break; \
case 2: \
- __put_mem_asm("strh", "sttrh", "%w", __pu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __put_mem_asm(str "h", "%w", __pu_val, (ptr), (err)); \
break; \
case 4: \
- __put_mem_asm("str", "sttr", "%w", __pu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __put_mem_asm(str, "%w", __pu_val, (ptr), (err)); \
break; \
case 8: \
- __put_mem_asm("str", "sttr", "%x", __pu_val, (ptr), \
- (err), ARM64_HAS_UAO); \
+ __put_mem_asm(str, "%x", __pu_val, (ptr), (err)); \
break; \
default: \
BUILD_BUG(); \
@@ -366,7 +368,7 @@ do { \
#define __raw_put_user(x, ptr, err) \
do { \
uaccess_enable_not_uao(); \
- __raw_put_mem(x, ptr, err); \
+ __raw_put_mem("sttr", x, ptr, err); \
uaccess_disable_not_uao(); \
} while (0)

@@ -391,6 +393,16 @@ do { \

#define put_user __put_user

+#define __put_kernel_nofault(dst, src, type, err_label) \
+do { \
+ int __pkn_err; \
+ \
+ __raw_put_mem("str", *((type *)(src)), \
+ (__force type __user *)(dst), __pkn_err); \
+ if (unlikely(__pkn_err)) \
+ goto err_label; \
+} while(0)
+
extern unsigned long __must_check __arch_copy_from_user(void *to, const void __user *from, unsigned long n);
#define raw_copy_from_user(to, from, n) \
({ \