lkml.org 
[lkml]   [2018]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.18 098/197] powerpc/uaccess: Enable get_user(u64, *p) on 32-bit
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Ellerman <mpe@ellerman.id.au>

[ Upstream commit f7a6947cd49b7ff4e03f1b4f7e7b223003d752ca ]

Currently if you build a 32-bit powerpc kernel and use get_user() to
load a u64 value it will fail to build with eg:

kernel/rseq.o: In function `rseq_get_rseq_cs':
kernel/rseq.c:123: undefined reference to `__get_user_bad'

This is hitting the check in __get_user_size() that makes sure the
size we're copying doesn't exceed the size of the destination:

#define __get_user_size(x, ptr, size, retval)
do {
retval = 0;
__chk_user_ptr(ptr);
if (size > sizeof(x))
(x) = __get_user_bad();

Which doesn't immediately make sense because the size of the
destination is u64, but it's not really, because __get_user_check()
etc. internally create an unsigned long and copy into that:

#define __get_user_check(x, ptr, size)
({
long __gu_err = -EFAULT;
unsigned long __gu_val = 0;

The problem being that on 32-bit unsigned long is not big enough to
hold a u64. We can fix this with a trick from hpa in the x86 code, we
statically check the type of x and set the type of __gu_val to either
unsigned long or unsigned long long.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/include/asm/uaccess.h | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -250,10 +250,17 @@ do { \
} \
} while (0)

+/*
+ * This is a type: either unsigned long, if the argument fits into
+ * that type, or otherwise unsigned long long.
+ */
+#define __long_type(x) \
+ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
+
#define __get_user_nocheck(x, ptr, size) \
({ \
long __gu_err; \
- unsigned long __gu_val; \
+ __long_type(*(ptr)) __gu_val; \
const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
__chk_user_ptr(ptr); \
if (!is_kernel_addr((unsigned long)__gu_addr)) \
@@ -267,7 +274,7 @@ do { \
#define __get_user_check(x, ptr, size) \
({ \
long __gu_err = -EFAULT; \
- unsigned long __gu_val = 0; \
+ __long_type(*(ptr)) __gu_val = 0; \
const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
might_fault(); \
if (access_ok(VERIFY_READ, __gu_addr, (size))) { \
@@ -281,7 +288,7 @@ do { \
#define __get_user_nosleep(x, ptr, size) \
({ \
long __gu_err; \
- unsigned long __gu_val; \
+ __long_type(*(ptr)) __gu_val; \
const __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
__chk_user_ptr(ptr); \
barrier_nospec(); \

\
 
 \ /
  Last update: 2018-09-13 16:09    [W:0.715 / U:1.608 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site