Re: [RFC PATCH v1 01/10] s390/uaccess: Add storage key checked access to user memory
From: Janosch Frank
Date: Tue Jan 18 2022 - 08:18:58 EST
On 1/18/22 10:52, Janis Schoetterl-Glausch wrote:
KVM needs a mechanism to do accesses to guest memory that honor
storage key protection.
Since the copy_to/from_user implementation makes use of move
instructions that support having an additional access key supplied,
we can implement __copy_from/to_user_with_key by enhancing the
existing implementation.
Signed-off-by: Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx>
For this I'd like to have buy-in from the kernel maintainers.
The patch looks good to me but currently I don't understand all of the
background so:
Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
---
arch/s390/include/asm/uaccess.h | 32 ++++++++++++++++++
arch/s390/lib/uaccess.c | 57 +++++++++++++++++++++++----------
2 files changed, 72 insertions(+), 17 deletions(-)
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index 02b467461163..5138040348cc 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -33,6 +33,38 @@ static inline int __range_ok(unsigned long addr, unsigned long size)
#define access_ok(addr, size) __access_ok(addr, size)
+unsigned long __must_check
+raw_copy_from_user_with_key(void *to, const void __user *from, unsigned long n,
+ char key);
+
+unsigned long __must_check
+raw_copy_to_user_with_key(void __user *to, const void *from, unsigned long n,
+ char key);
+
+static __always_inline __must_check unsigned long
+__copy_from_user_with_key(void *to, const void __user *from, unsigned long n,
+ char key)
+{
+ might_fault();
+ if (should_fail_usercopy())
+ return n;
+ instrument_copy_from_user(to, from, n);
+ check_object_size(to, n, false);
+ return raw_copy_from_user_with_key(to, from, n, key);
+}
+
+static __always_inline __must_check unsigned long
+__copy_to_user_with_key(void __user *to, const void *from, unsigned long n,
+ char key)
+{
+ might_fault();
+ if (should_fail_usercopy())
+ return n;
+ instrument_copy_to_user(to, from, n);
+ check_object_size(from, n, true);
+ return raw_copy_to_user_with_key(to, from, n, key);
+}
+
unsigned long __must_check
raw_copy_from_user(void *to, const void __user *from, unsigned long n);
diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
index d3a700385875..ce7a150dd93a 100644
--- a/arch/s390/lib/uaccess.c
+++ b/arch/s390/lib/uaccess.c
@@ -59,11 +59,13 @@ static inline int copy_with_mvcos(void)
#endif
static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr,
- unsigned long size)
+ unsigned long size, char key)
{
unsigned long tmp1, tmp2;
union oac spec = {
+ .oac2.key = key,
.oac2.as = PSW_BITS_AS_SECONDARY,
+ .oac2.k = 1,
.oac2.a = 1,
};
@@ -94,19 +96,19 @@ static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr
}
static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
- unsigned long size)
+ unsigned long size, char key)
{
unsigned long tmp1, tmp2;
tmp1 = -256UL;
asm volatile(
" sacf 0\n"
- "0: mvcp 0(%0,%2),0(%1),%3\n"
+ "0: mvcp 0(%0,%2),0(%1),%[key]\n"
"7: jz 5f\n"
"1: algr %0,%3\n"
" la %1,256(%1)\n"
" la %2,256(%2)\n"
- "2: mvcp 0(%0,%2),0(%1),%3\n"
+ "2: mvcp 0(%0,%2),0(%1),%[key]\n"
"8: jnz 1b\n"
" j 5f\n"
"3: la %4,255(%1)\n" /* %4 = ptr + 255 */
@@ -115,7 +117,7 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
" slgr %4,%1\n"
" clgr %0,%4\n" /* copy crosses next page boundary? */
" jnh 6f\n"
- "4: mvcp 0(%4,%2),0(%1),%3\n"
+ "4: mvcp 0(%4,%2),0(%1),%[key]\n"
"9: slgr %0,%4\n"
" j 6f\n"
"5: slgr %0,%0\n"
@@ -123,24 +125,36 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,6b)
EX_TABLE(7b,3b) EX_TABLE(8b,3b) EX_TABLE(9b,6b)
: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
- : : "cc", "memory");
+ : [key] "d" (key << 4)
+ : "cc", "memory");
return size;
}
unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n)
{
if (copy_with_mvcos())
- return copy_from_user_mvcos(to, from, n);
- return copy_from_user_mvcp(to, from, n);
+ return copy_from_user_mvcos(to, from, n, 0);
+ return copy_from_user_mvcp(to, from, n, 0);
}
EXPORT_SYMBOL(raw_copy_from_user);
-static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
- unsigned long size)
+unsigned long raw_copy_from_user_with_key(void *to, const void __user *from,
+ unsigned long n, char key)
+{
+ if (copy_with_mvcos())
+ return copy_from_user_mvcos(to, from, n, key);
+ return copy_from_user_mvcp(to, from, n, key);
+}
+EXPORT_SYMBOL(raw_copy_from_user_with_key);
+
+inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
+ unsigned long size, char key)
{
unsigned long tmp1, tmp2;
union oac spec = {
+ .oac1.key = key,
.oac1.as = PSW_BITS_AS_SECONDARY,
+ .oac1.k = 1,
.oac1.a = 1,
};
@@ -171,19 +185,19 @@ static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
}
static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
- unsigned long size)
+ unsigned long size, char key)
{
unsigned long tmp1, tmp2;
tmp1 = -256UL;
asm volatile(
" sacf 0\n"
- "0: mvcs 0(%0,%1),0(%2),%3\n"
+ "0: mvcs 0(%0,%1),0(%2),%[key]\n"
"7: jz 5f\n"
"1: algr %0,%3\n"
" la %1,256(%1)\n"
" la %2,256(%2)\n"
- "2: mvcs 0(%0,%1),0(%2),%3\n"
+ "2: mvcs 0(%0,%1),0(%2),%[key]\n"
"8: jnz 1b\n"
" j 5f\n"
"3: la %4,255(%1)\n" /* %4 = ptr + 255 */
@@ -192,7 +206,7 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
" slgr %4,%1\n"
" clgr %0,%4\n" /* copy crosses next page boundary? */
" jnh 6f\n"
- "4: mvcs 0(%4,%1),0(%2),%3\n"
+ "4: mvcs 0(%4,%1),0(%2),%[key]\n"
"9: slgr %0,%4\n"
" j 6f\n"
"5: slgr %0,%0\n"
@@ -200,17 +214,26 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,6b)
EX_TABLE(7b,3b) EX_TABLE(8b,3b) EX_TABLE(9b,6b)
: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
- : : "cc", "memory");
+ : [key] "d" (key << 4)
+ : "cc", "memory");
return size;
}
unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n)
{
if (copy_with_mvcos())
- return copy_to_user_mvcos(to, from, n);
- return copy_to_user_mvcs(to, from, n);
+ return copy_to_user_mvcos(to, from, n, 0);
+ return copy_to_user_mvcs(to, from, n, 0);
}
EXPORT_SYMBOL(raw_copy_to_user);
+unsigned long raw_copy_to_user_with_key(void __user *to, const void *from,
+ unsigned long n, char key)
+{
+ if (copy_with_mvcos())
+ return copy_to_user_mvcos(to, from, n, key);
+ return copy_to_user_mvcs(to, from, n, key);
+}
+EXPORT_SYMBOL(raw_copy_to_user_with_key);
static inline unsigned long clear_user_mvcos(void __user *to, unsigned long size)
{