s390/uaccess: rework uaccess code - fix locking issues

The current uaccess code uses a page table walk in some circumstances,
e.g. in case of the in atomic futex operations or if running on old
hardware which doesn't support the mvcos instruction.

However it turned out that the page table walk code does not correctly
lock page tables when accessing page table entries.
In other words: a different cpu may invalidate a page table entry while
the current cpu inspects the pte. This may lead to random data corruption.

Adding correct locking however isn't trivial for all uaccess operations.
Especially copy_in_user() is problematic since that requires to hold at
least two locks, but must be protected against ABBA deadlock when a
different cpu also performs a copy_in_user() operation.

So the solution is a different approach where we change address spaces:

User space runs in primary address mode, or access register mode within
vdso code, like it currently already does.

The kernel usually also runs in home space mode, however when accessing
user space the kernel switches to primary or secondary address mode if
the mvcos instruction is not available or if a compare-and-swap (futex)
instruction on a user space address is performed.
KVM however is special, since that requires the kernel to run in home
address space while implicitly accessing user space with the sie
instruction.

So we end up with:

User space:
- runs in primary or access register mode
- cr1 contains the user asce
- cr7 contains the user asce
- cr13 contains the kernel asce

Kernel space:
- runs in home space mode
- cr1 contains the user or kernel asce
  -> the kernel asce is loaded when a uaccess requires primary or
     secondary address mode
- cr7 contains the user or kernel asce, (changed with set_fs())
- cr13 contains the kernel asce

In case of uaccess the kernel changes to:
- primary space mode in case of a uaccess (copy_to_user) and uses
  e.g. the mvcp instruction to access user space. However the kernel
  will stay in home space mode if the mvcos instruction is available
- secondary space mode in case of futex atomic operations, so that the
  instructions come from primary address space and data from secondary
  space

In case of kvm the kernel runs in home space mode, but cr1 gets switched
to contain the gmap asce before the sie instruction gets executed. When
the sie instruction is finished cr1 will be switched back to contain the
user asce.

A context switch between two processes will always load the kernel asce
for the next process in cr1. So the first exit to user space is a bit
more expensive (one extra load control register instruction) than before,
however keeps the code rather simple.

In sum this means there is no need to perform any error prone page table
walks anymore when accessing user space.

The patch seems to be rather large, however it mainly removes the
the page table walk code and restores the previously deleted "standard"
uaccess code, with a couple of changes.

The uaccess without mvcos mode can be enforced with the "uaccess_primary"
kernel parameter.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 407 insertions, 0 deletions

diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
new file mode 100644
index 000000000000..23f866b4c7f1
--- /dev/null
+++ b/arch/s390/lib/uaccess.c
@@ -0,0 +1,407 @@
+/*
+ *  Standard user space access functions based on mvcp/mvcs and doing
+ *  interesting things in the secondary space mode.
+ *
+ *    Copyright IBM Corp. 2006,2014
+ *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com),
+ *		 Gerald Schaefer (gerald.schaefer@de.ibm.com)
+ */
+
+#include <linux/jump_label.h>
+#include <linux/uaccess.h>
+#include <linux/export.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <asm/mmu_context.h>
+#include <asm/facility.h>
+
+#ifndef CONFIG_64BIT
+#define AHI	"ahi"
+#define ALR	"alr"
+#define CLR	"clr"
+#define LHI	"lhi"
+#define SLR	"slr"
+#else
+#define AHI	"aghi"
+#define ALR	"algr"
+#define CLR	"clgr"
+#define LHI	"lghi"
+#define SLR	"slgr"
+#endif
+
+static struct static_key have_mvcos = STATIC_KEY_INIT_FALSE;
+
+static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr,
+						 unsigned long size)
+{
+	register unsigned long reg0 asm("0") = 0x81UL;
+	unsigned long tmp1, tmp2;
+
+	tmp1 = -4096UL;
+	asm volatile(
+		"0: .insn ss,0xc80000000000,0(%0,%2),0(%1),0\n"
+		"9: jz    7f\n"
+		"1:"ALR"  %0,%3\n"
+		"  "SLR"  %1,%3\n"
+		"  "SLR"  %2,%3\n"
+		"   j     0b\n"
+		"2: la    %4,4095(%1)\n"/* %4 = ptr + 4095 */
+		"   nr    %4,%3\n"	/* %4 = (ptr + 4095) & -4096 */
+		"  "SLR"  %4,%1\n"
+		"  "CLR"  %0,%4\n"	/* copy crosses next page boundary? */
+		"   jnh   4f\n"
+		"3: .insn ss,0xc80000000000,0(%4,%2),0(%1),0\n"
+		"10:"SLR"  %0,%4\n"
+		"  "ALR"  %2,%4\n"
+		"4:"LHI"  %4,-1\n"
+		"  "ALR"  %4,%0\n"	/* copy remaining size, subtract 1 */
+		"   bras  %3,6f\n"	/* memset loop */
+		"   xc    0(1,%2),0(%2)\n"
+		"5: xc    0(256,%2),0(%2)\n"
+		"   la    %2,256(%2)\n"
+		"6:"AHI"  %4,-256\n"
+		"   jnm   5b\n"
+		"   ex    %4,0(%3)\n"
+		"   j     8f\n"
+		"7:"SLR"  %0,%0\n"
+		"8:\n"
+		EX_TABLE(0b,2b) EX_TABLE(3b,4b) EX_TABLE(9b,2b) EX_TABLE(10b,4b)
+		: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
+		: "d" (reg0) : "cc", "memory");
+	return size;
+}
+
+static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
+						unsigned long size)
+{
+	unsigned long tmp1, tmp2;
+
+	update_primary_asce(current);
+	tmp1 = -256UL;
+	asm volatile(
+		"   sacf  0\n"
+		"0: mvcp  0(%0,%2),0(%1),%3\n"
+		"10:jz    8f\n"
+		"1:"ALR"  %0,%3\n"
+		"   la    %1,256(%1)\n"
+		"   la    %2,256(%2)\n"
+		"2: mvcp  0(%0,%2),0(%1),%3\n"
+		"11:jnz   1b\n"
+		"   j     8f\n"
+		"3: la    %4,255(%1)\n"	/* %4 = ptr + 255 */
+		"  "LHI"  %3,-4096\n"
+		"   nr    %4,%3\n"	/* %4 = (ptr + 255) & -4096 */
+		"  "SLR"  %4,%1\n"
+		"  "CLR"  %0,%4\n"	/* copy crosses next page boundary? */
+		"   jnh   5f\n"
+		"4: mvcp  0(%4,%2),0(%1),%3\n"
+		"12:"SLR"  %0,%4\n"
+		"  "ALR"  %2,%4\n"
+		"5:"LHI"  %4,-1\n"
+		"  "ALR"  %4,%0\n"	/* copy remaining size, subtract 1 */
+		"   bras  %3,7f\n"	/* memset loop */
+		"   xc    0(1,%2),0(%2)\n"
+		"6: xc    0(256,%2),0(%2)\n"
+		"   la    %2,256(%2)\n"
+		"7:"AHI"  %4,-256\n"
+		"   jnm   6b\n"
+		"   ex    %4,0(%3)\n"
+		"   j     9f\n"
+		"8:"SLR"  %0,%0\n"
+		"9: sacf  768\n"
+		EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,5b)
+		EX_TABLE(10b,3b) EX_TABLE(11b,3b) EX_TABLE(12b,5b)
+		: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
+		: : "cc", "memory");
+	return size;
+}
+
+unsigned long __copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	if (static_key_false(&have_mvcos))
+		return copy_from_user_mvcos(to, from, n);
+	return copy_from_user_mvcp(to, from, n);
+}
+EXPORT_SYMBOL(__copy_from_user);
+
+static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
+					       unsigned long size)
+{
+	register unsigned long reg0 asm("0") = 0x810000UL;
+	unsigned long tmp1, tmp2;
+
+	tmp1 = -4096UL;
+	asm volatile(
+		"0: .insn ss,0xc80000000000,0(%0,%1),0(%2),0\n"
+		"6: jz    4f\n"
+		"1:"ALR"  %0,%3\n"
+		"  "SLR"  %1,%3\n"
+		"  "SLR"  %2,%3\n"
+		"   j     0b\n"
+		"2: la    %4,4095(%1)\n"/* %4 = ptr + 4095 */
+		"   nr    %4,%3\n"	/* %4 = (ptr + 4095) & -4096 */
+		"  "SLR"  %4,%1\n"
+		"  "CLR"  %0,%4\n"	/* copy crosses next page boundary? */
+		"   jnh   5f\n"
+		"3: .insn ss,0xc80000000000,0(%4,%1),0(%2),0\n"
+		"7:"SLR"  %0,%4\n"
+		"   j     5f\n"
+		"4:"SLR"  %0,%0\n"
+		"5:\n"
+		EX_TABLE(0b,2b) EX_TABLE(3b,5b) EX_TABLE(6b,2b) EX_TABLE(7b,5b)
+		: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
+		: "d" (reg0) : "cc", "memory");
+	return size;
+}
+
+static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
+					      unsigned long size)
+{
+	unsigned long tmp1, tmp2;
+
+	update_primary_asce(current);
+	tmp1 = -256UL;
+	asm volatile(
+		"   sacf  0\n"
+		"0: mvcs  0(%0,%1),0(%2),%3\n"
+		"7: jz    5f\n"
+		"1:"ALR"  %0,%3\n"
+		"   la    %1,256(%1)\n"
+		"   la    %2,256(%2)\n"
+		"2: mvcs  0(%0,%1),0(%2),%3\n"
+		"8: jnz   1b\n"
+		"   j     5f\n"
+		"3: la    %4,255(%1)\n" /* %4 = ptr + 255 */
+		"  "LHI"  %3,-4096\n"
+		"   nr    %4,%3\n"	/* %4 = (ptr + 255) & -4096 */
+		"  "SLR"  %4,%1\n"
+		"  "CLR"  %0,%4\n"	/* copy crosses next page boundary? */
+		"   jnh   6f\n"
+		"4: mvcs  0(%4,%1),0(%2),%3\n"
+		"9:"SLR"  %0,%4\n"
+		"   j     6f\n"
+		"5:"SLR"  %0,%0\n"
+		"6: sacf  768\n"
+		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");
+	return size;
+}
+
+unsigned long __copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	if (static_key_false(&have_mvcos))
+		return copy_to_user_mvcos(to, from, n);
+	return copy_to_user_mvcs(to, from, n);
+}
+EXPORT_SYMBOL(__copy_to_user);
+
+static inline unsigned long copy_in_user_mvcos(void __user *to, const void __user *from,
+					       unsigned long size)
+{
+	register unsigned long reg0 asm("0") = 0x810081UL;
+	unsigned long tmp1, tmp2;
+
+	tmp1 = -4096UL;
+	/* FIXME: copy with reduced length. */
+	asm volatile(
+		"0: .insn ss,0xc80000000000,0(%0,%1),0(%2),0\n"
+		"   jz	  2f\n"
+		"1:"ALR"  %0,%3\n"
+		"  "SLR"  %1,%3\n"
+		"  "SLR"  %2,%3\n"
+		"   j	  0b\n"
+		"2:"SLR"  %0,%0\n"
+		"3: \n"
+		EX_TABLE(0b,3b)
+		: "+a" (size), "+a" (to), "+a" (from), "+a" (tmp1), "=a" (tmp2)
+		: "d" (reg0) : "cc", "memory");
+	return size;
+}
+
+static inline unsigned long copy_in_user_mvc(void __user *to, const void __user *from,
+					     unsigned long size)
+{
+	unsigned long tmp1;
+
+	update_primary_asce(current);
+	asm volatile(
+		"   sacf  256\n"
+		"  "AHI"  %0,-1\n"
+		"   jo	  5f\n"
+		"   bras  %3,3f\n"
+		"0:"AHI"  %0,257\n"
+		"1: mvc	  0(1,%1),0(%2)\n"
+		"   la	  %1,1(%1)\n"
+		"   la	  %2,1(%2)\n"
+		"  "AHI"  %0,-1\n"
+		"   jnz	  1b\n"
+		"   j	  5f\n"
+		"2: mvc	  0(256,%1),0(%2)\n"
+		"   la	  %1,256(%1)\n"
+		"   la	  %2,256(%2)\n"
+		"3:"AHI"  %0,-256\n"
+		"   jnm	  2b\n"
+		"4: ex	  %0,1b-0b(%3)\n"
+		"5: "SLR"  %0,%0\n"
+		"6: sacf  768\n"
+		EX_TABLE(1b,6b) EX_TABLE(2b,0b) EX_TABLE(4b,0b)
+		: "+a" (size), "+a" (to), "+a" (from), "=a" (tmp1)
+		: : "cc", "memory");
+	return size;
+}
+
+unsigned long __copy_in_user(void __user *to, const void __user *from, unsigned long n)
+{
+	if (static_key_false(&have_mvcos))
+		return copy_in_user_mvcos(to, from, n);
+	return copy_in_user_mvc(to, from, n);
+}
+EXPORT_SYMBOL(__copy_in_user);
+
+static inline unsigned long clear_user_mvcos(void __user *to, unsigned long size)
+{
+	register unsigned long reg0 asm("0") = 0x810000UL;
+	unsigned long tmp1, tmp2;
+
+	tmp1 = -4096UL;
+	asm volatile(
+		"0: .insn ss,0xc80000000000,0(%0,%1),0(%4),0\n"
+		"   jz	  4f\n"
+		"1:"ALR"  %0,%2\n"
+		"  "SLR"  %1,%2\n"
+		"   j	  0b\n"
+		"2: la	  %3,4095(%1)\n"/* %4 = to + 4095 */
+		"   nr	  %3,%2\n"	/* %4 = (to + 4095) & -4096 */
+		"  "SLR"  %3,%1\n"
+		"  "CLR"  %0,%3\n"	/* copy crosses next page boundary? */
+		"   jnh	  5f\n"
+		"3: .insn ss,0xc80000000000,0(%3,%1),0(%4),0\n"
+		"  "SLR"  %0,%3\n"
+		"   j	  5f\n"
+		"4:"SLR"  %0,%0\n"
+		"5:\n"
+		EX_TABLE(0b,2b) EX_TABLE(3b,5b)
+		: "+a" (size), "+a" (to), "+a" (tmp1), "=a" (tmp2)
+		: "a" (empty_zero_page), "d" (reg0) : "cc", "memory");
+	return size;
+}
+
+static inline unsigned long clear_user_xc(void __user *to, unsigned long size)
+{
+	unsigned long tmp1, tmp2;
+
+	update_primary_asce(current);
+	asm volatile(
+		"   sacf  256\n"
+		"  "AHI"  %0,-1\n"
+		"   jo    5f\n"
+		"   bras  %3,3f\n"
+		"   xc    0(1,%1),0(%1)\n"
+		"0:"AHI"  %0,257\n"
+		"   la    %2,255(%1)\n" /* %2 = ptr + 255 */
+		"   srl   %2,12\n"
+		"   sll   %2,12\n"	/* %2 = (ptr + 255) & -4096 */
+		"  "SLR"  %2,%1\n"
+		"  "CLR"  %0,%2\n"	/* clear crosses next page boundary? */
+		"   jnh   5f\n"
+		"  "AHI"  %2,-1\n"
+		"1: ex    %2,0(%3)\n"
+		"  "AHI"  %2,1\n"
+		"  "SLR"  %0,%2\n"
+		"   j     5f\n"
+		"2: xc    0(256,%1),0(%1)\n"
+		"   la    %1,256(%1)\n"
+		"3:"AHI"  %0,-256\n"
+		"   jnm   2b\n"
+		"4: ex    %0,0(%3)\n"
+		"5: "SLR"  %0,%0\n"
+		"6: sacf  768\n"
+		EX_TABLE(1b,6b) EX_TABLE(2b,0b) EX_TABLE(4b,0b)
+		: "+a" (size), "+a" (to), "=a" (tmp1), "=a" (tmp2)
+		: : "cc", "memory");
+	return size;
+}
+
+unsigned long __clear_user(void __user *to, unsigned long size)
+{
+	if (static_key_false(&have_mvcos))
+			return clear_user_mvcos(to, size);
+	return clear_user_xc(to, size);
+}
+EXPORT_SYMBOL(__clear_user);
+
+static inline unsigned long strnlen_user_srst(const char __user *src,
+					      unsigned long size)
+{
+	register unsigned long reg0 asm("0") = 0;
+	unsigned long tmp1, tmp2;
+
+	if (unlikely(!size))
+		return 0;
+	update_primary_asce(current);
+	asm volatile(
+		"   la    %2,0(%1)\n"
+		"   la    %3,0(%0,%1)\n"
+		"  "SLR"  %0,%0\n"
+		"   sacf  256\n"
+		"0: srst  %3,%2\n"
+		"   jo    0b\n"
+		"   la    %0,1(%3)\n"	/* strnlen_user results includes \0 */
+		"  "SLR"  %0,%1\n"
+		"1: sacf  768\n"
+		EX_TABLE(0b,1b)
+		: "+a" (size), "+a" (src), "=a" (tmp1), "=a" (tmp2)
+		: "d" (reg0) : "cc", "memory");
+	return size;
+}
+
+unsigned long __strnlen_user(const char __user *src, unsigned long size)
+{
+	update_primary_asce(current);
+	return strnlen_user_srst(src, size);
+}
+EXPORT_SYMBOL(__strnlen_user);
+
+long __strncpy_from_user(char *dst, const char __user *src, long size)
+{
+	size_t done, len, offset, len_str;
+
+	if (unlikely(size <= 0))
+		return 0;
+	done = 0;
+	do {
+		offset = (size_t)src & ~PAGE_MASK;
+		len = min(size - done, PAGE_SIZE - offset);
+		if (copy_from_user(dst, src, len))
+			return -EFAULT;
+		len_str = strnlen(dst, len);
+		done += len_str;
+		src += len_str;
+		dst += len_str;
+	} while ((len_str == len) && (done < size));
+	return done;
+}
+EXPORT_SYMBOL(__strncpy_from_user);
+
+/*
+ * The "old" uaccess variant without mvcos can be enforced with the
+ * uaccess_primary kernel parameter. This is mainly for debugging purposes.
+ */
+static int uaccess_primary __initdata;
+
+static int __init parse_uaccess_pt(char *__unused)
+{
+	uaccess_primary = 1;
+	return 0;
+}
+early_param("uaccess_primary", parse_uaccess_pt);
+
+static int __init uaccess_init(void)
+{
+	if (IS_ENABLED(CONFIG_64BIT) && !uaccess_primary && test_facility(27))
+		static_key_slow_inc(&have_mvcos);
+	return 0;
+}
+early_initcall(uaccess_init);