lkml.org 
[lkml]   [2021]   [Feb]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] powerpc/uaccess: Perform barrier_nospec() in KUAP allowance helpers
Date
barrier_nospec() in uaccess helpers is there to protect against
speculative accesses around access_ok().

When using user_access_begin() sequences together with
unsafe_get_user() like macros, barrier_nospec() is called for
every single read although we know the access_ok() is done
onece.

Since all user accesses must be granted by a call to either
allow_read_from_user() or allow_read_write_user() which will
always happen after the access_ok() check, move the barrier_nospec()
there.

Reported-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/include/asm/kup.h | 2 ++
arch/powerpc/include/asm/uaccess.h | 12 +-----------
2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index bf221a2a523e..7ec21af49a45 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -91,6 +91,7 @@ static __always_inline void setup_kup(void)

static inline void allow_read_from_user(const void __user *from, unsigned long size)
{
+ barrier_nospec();
allow_user_access(NULL, from, size, KUAP_READ);
}

@@ -102,6 +103,7 @@ static inline void allow_write_to_user(void __user *to, unsigned long size)
static inline void allow_read_write_user(void __user *to, const void __user *from,
unsigned long size)
{
+ barrier_nospec();
allow_user_access(to, from, size, KUAP_READ_WRITE);
}

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 501c9a79038c..46123ae6a4c9 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -315,7 +315,6 @@ do { \
__chk_user_ptr(__gu_addr); \
if (!is_kernel_addr((unsigned long)__gu_addr)) \
might_fault(); \
- barrier_nospec(); \
if (do_allow) \
__get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \
else \
@@ -333,10 +332,8 @@ do { \
__typeof__(size) __gu_size = (size); \
\
might_fault(); \
- if (access_ok(__gu_addr, __gu_size)) { \
- barrier_nospec(); \
+ if (access_ok(__gu_addr, __gu_size)) \
__get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \
- } \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
\
__gu_err; \
@@ -350,7 +347,6 @@ do { \
__typeof__(size) __gu_size = (size); \
\
__chk_user_ptr(__gu_addr); \
- barrier_nospec(); \
__get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
\
@@ -395,7 +391,6 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
{
unsigned long ret;

- barrier_nospec();
allow_read_write_user(to, from, n);
ret = __copy_tofrom_user(to, from, n);
prevent_read_write_user(to, from, n);
@@ -412,19 +407,15 @@ static inline unsigned long raw_copy_from_user(void *to,

switch (n) {
case 1:
- barrier_nospec();
__get_user_size(*(u8 *)to, from, 1, ret);
break;
case 2:
- barrier_nospec();
__get_user_size(*(u16 *)to, from, 2, ret);
break;
case 4:
- barrier_nospec();
__get_user_size(*(u32 *)to, from, 4, ret);
break;
case 8:
- barrier_nospec();
__get_user_size(*(u64 *)to, from, 8, ret);
break;
}
@@ -432,7 +423,6 @@ static inline unsigned long raw_copy_from_user(void *to,
return 0;
}

- barrier_nospec();
allow_read_from_user(from, n);
ret = __copy_tofrom_user((__force void __user *)to, from, n);
prevent_read_from_user(from, n);
--
2.25.0
\
 
 \ /
  Last update: 2021-02-07 11:11    [W:0.044 / U:1.504 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site