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Date: Tue, 18 Jan 2022 14:18:40 +0100
From: Janosch Frank <frankja@...ux.ibm.com>
To: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Nico Boehr <nrb@...ux.ibm.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>,
linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 01/10] s390/uaccess: Add storage key checked access
to user memory
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@...ux.ibm.com>
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@...ux.ibm.com>
> ---
> 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)
> {
>
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