[PATCH 5.6 105/126] s390/pci: Fix s390_mmio_read/write with MIO - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Niklas Schnelle <schnelle@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>
Subject: [PATCH 5.6 105/126] s390/pci: Fix s390_mmio_read/write with MIO
Date: Tue, 26 May 2020 20:54:02 +0200	[thread overview]
Message-ID: <20200526183946.480389842@linuxfoundation.org> (raw)
In-Reply-To: <20200526183937.471379031@linuxfoundation.org>

From: Niklas Schnelle <schnelle@linux.ibm.com>

commit f058599e22d59e594e5aae1dc10560568d8f4a8b upstream.

The s390_mmio_read/write syscalls are currently broken when running with
MIO.

The new pcistb_mio/pcstg_mio/pcilg_mio instructions are executed
similiarly to normal load/store instructions and do address translation
in the current address space. That means inside the kernel they are
aware of mappings into kernel address space while outside the kernel
they use user space mappings (usually created through mmap'ing a PCI
device file).

Now when existing user space applications use the s390_pci_mmio_write
and s390_pci_mmio_read syscalls, they pass I/O addresses that are mapped
into user space so as to be usable with the new instructions without
needing a syscall. Accessing these addresses with the old instructions
as done currently leads to a kernel panic.

Also, for such a user space mapping there may not exist an equivalent
kernel space mapping which means we can't just use the new instructions
in kernel space.

Instead of replicating user mappings in the kernel which then might
collide with other mappings, we can conceptually execute the new
instructions as if executed by the user space application using the
secondary address space. This even allows us to directly store to the
user pointer without the need for copy_to/from_user().

Cc: stable@vger.kernel.org
Fixes: 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/include/asm/pci_io.h |   10 +
 arch/s390/pci/pci_mmio.c       |  213 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 219 insertions(+), 4 deletions(-)

--- a/arch/s390/include/asm/pci_io.h
+++ b/arch/s390/include/asm/pci_io.h
@@ -8,6 +8,10 @@
 #include <linux/slab.h>
 #include <asm/pci_insn.h>
 
+/* I/O size constraints */
+#define ZPCI_MAX_READ_SIZE	8
+#define ZPCI_MAX_WRITE_SIZE	128
+
 /* I/O Map */
 #define ZPCI_IOMAP_SHIFT		48
 #define ZPCI_IOMAP_ADDR_BASE		0x8000000000000000UL
@@ -140,7 +144,8 @@ static inline int zpci_memcpy_fromio(voi
 
 	while (n > 0) {
 		size = zpci_get_max_write_size((u64 __force) src,
-					       (u64) dst, n, 8);
+					       (u64) dst, n,
+					       ZPCI_MAX_READ_SIZE);
 		rc = zpci_read_single(dst, src, size);
 		if (rc)
 			break;
@@ -161,7 +166,8 @@ static inline int zpci_memcpy_toio(volat
 
 	while (n > 0) {
 		size = zpci_get_max_write_size((u64 __force) dst,
-					       (u64) src, n, 128);
+					       (u64) src, n,
+					       ZPCI_MAX_WRITE_SIZE);
 		if (size > 8) /* main path */
 			rc = zpci_write_block(dst, src, size);
 		else
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c
@@ -11,6 +11,113 @@
 #include <linux/mm.h>
 #include <linux/errno.h>
 #include <linux/pci.h>
+#include <asm/pci_io.h>
+#include <asm/pci_debug.h>
+
+static inline void zpci_err_mmio(u8 cc, u8 status, u64 offset)
+{
+	struct {
+		u64 offset;
+		u8 cc;
+		u8 status;
+	} data = {offset, cc, status};
+
+	zpci_err_hex(&data, sizeof(data));
+}
+
+static inline int __pcistb_mio_inuser(
+		void __iomem *ioaddr, const void __user *src,
+		u64 len, u8 *status)
+{
+	int cc = -ENXIO;
+
+	asm volatile (
+		"       sacf 256\n"
+		"0:     .insn   rsy,0xeb00000000d4,%[len],%[ioaddr],%[src]\n"
+		"1:     ipm     %[cc]\n"
+		"       srl     %[cc],28\n"
+		"2:     sacf 768\n"
+		EX_TABLE(0b, 2b) EX_TABLE(1b, 2b)
+		: [cc] "+d" (cc), [len] "+d" (len)
+		: [ioaddr] "a" (ioaddr), [src] "Q" (*((u8 __force *)src))
+		: "cc", "memory");
+	*status = len >> 24 & 0xff;
+	return cc;
+}
+
+static inline int __pcistg_mio_inuser(
+		void __iomem *ioaddr, const void __user *src,
+		u64 ulen, u8 *status)
+{
+	register u64 addr asm("2") = (u64 __force) ioaddr;
+	register u64 len asm("3") = ulen;
+	int cc = -ENXIO;
+	u64 val = 0;
+	u64 cnt = ulen;
+	u8 tmp;
+
+	/*
+	 * copy 0 < @len <= 8 bytes from @src into the right most bytes of
+	 * a register, then store it to PCI at @ioaddr while in secondary
+	 * address space. pcistg then uses the user mappings.
+	 */
+	asm volatile (
+		"       sacf    256\n"
+		"0:     llgc    %[tmp],0(%[src])\n"
+		"       sllg    %[val],%[val],8\n"
+		"       aghi    %[src],1\n"
+		"       ogr     %[val],%[tmp]\n"
+		"       brctg   %[cnt],0b\n"
+		"1:     .insn   rre,0xb9d40000,%[val],%[ioaddr]\n"
+		"2:     ipm     %[cc]\n"
+		"       srl     %[cc],28\n"
+		"3:     sacf    768\n"
+		EX_TABLE(0b, 3b) EX_TABLE(1b, 3b) EX_TABLE(2b, 3b)
+		:
+		[src] "+a" (src), [cnt] "+d" (cnt),
+		[val] "+d" (val), [tmp] "=d" (tmp),
+		[len] "+d" (len), [cc] "+d" (cc),
+		[ioaddr] "+a" (addr)
+		:: "cc", "memory");
+	*status = len >> 24 & 0xff;
+
+	/* did we read everything from user memory? */
+	if (!cc && cnt != 0)
+		cc = -EFAULT;
+
+	return cc;
+}
+
+static inline int __memcpy_toio_inuser(void __iomem *dst,
+				   const void __user *src, size_t n)
+{
+	int size, rc = 0;
+	u8 status = 0;
+	mm_segment_t old_fs;
+
+	if (!src)
+		return -EINVAL;
+
+	old_fs = enable_sacf_uaccess();
+	while (n > 0) {
+		size = zpci_get_max_write_size((u64 __force) dst,
+					       (u64 __force) src, n,
+					       ZPCI_MAX_WRITE_SIZE);
+		if (size > 8) /* main path */
+			rc = __pcistb_mio_inuser(dst, src, size, &status);
+		else
+			rc = __pcistg_mio_inuser(dst, src, size, &status);
+		if (rc)
+			break;
+		src += size;
+		dst += size;
+		n -= size;
+	}
+	disable_sacf_uaccess(old_fs);
+	if (rc)
+		zpci_err_mmio(rc, status, (__force u64) dst);
+	return rc;
+}
 
 static long get_pfn(unsigned long user_addr, unsigned long access,
 		    unsigned long *pfn)
@@ -46,6 +153,20 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, uns
 
 	if (length <= 0 || PAGE_SIZE - (mmio_addr & ~PAGE_MASK) < length)
 		return -EINVAL;
+
+	/*
+	 * Only support read access to MIO capable devices on a MIO enabled
+	 * system. Otherwise we would have to check for every address if it is
+	 * a special ZPCI_ADDR and we would have to do a get_pfn() which we
+	 * don't need for MIO capable devices.
+	 */
+	if (static_branch_likely(&have_mio)) {
+		ret = __memcpy_toio_inuser((void  __iomem *) mmio_addr,
+					user_buffer,
+					length);
+		return ret;
+	}
+
 	if (length > 64) {
 		buf = kmalloc(length, GFP_KERNEL);
 		if (!buf)
@@ -56,7 +177,8 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, uns
 	ret = get_pfn(mmio_addr, VM_WRITE, &pfn);
 	if (ret)
 		goto out;
-	io_addr = (void __iomem *)((pfn << PAGE_SHIFT) | (mmio_addr & ~PAGE_MASK));
+	io_addr = (void __iomem *)((pfn << PAGE_SHIFT) |
+			(mmio_addr & ~PAGE_MASK));
 
 	ret = -EFAULT;
 	if ((unsigned long) io_addr < ZPCI_IOMAP_ADDR_BASE)
@@ -72,6 +194,78 @@ out:
 	return ret;
 }
 
+static inline int __pcilg_mio_inuser(
+		void __user *dst, const void __iomem *ioaddr,
+		u64 ulen, u8 *status)
+{
+	register u64 addr asm("2") = (u64 __force) ioaddr;
+	register u64 len asm("3") = ulen;
+	u64 cnt = ulen;
+	int shift = ulen * 8;
+	int cc = -ENXIO;
+	u64 val, tmp;
+
+	/*
+	 * read 0 < @len <= 8 bytes from the PCI memory mapped at @ioaddr (in
+	 * user space) into a register using pcilg then store these bytes at
+	 * user address @dst
+	 */
+	asm volatile (
+		"       sacf    256\n"
+		"0:     .insn   rre,0xb9d60000,%[val],%[ioaddr]\n"
+		"1:     ipm     %[cc]\n"
+		"       srl     %[cc],28\n"
+		"       ltr     %[cc],%[cc]\n"
+		"       jne     4f\n"
+		"2:     ahi     %[shift],-8\n"
+		"       srlg    %[tmp],%[val],0(%[shift])\n"
+		"3:     stc     %[tmp],0(%[dst])\n"
+		"       aghi    %[dst],1\n"
+		"       brctg   %[cnt],2b\n"
+		"4:     sacf    768\n"
+		EX_TABLE(0b, 4b) EX_TABLE(1b, 4b) EX_TABLE(3b, 4b)
+		:
+		[cc] "+d" (cc), [val] "=d" (val), [len] "+d" (len),
+		[dst] "+a" (dst), [cnt] "+d" (cnt), [tmp] "=d" (tmp),
+		[shift] "+d" (shift)
+		:
+		[ioaddr] "a" (addr)
+		: "cc", "memory");
+
+	/* did we write everything to the user space buffer? */
+	if (!cc && cnt != 0)
+		cc = -EFAULT;
+
+	*status = len >> 24 & 0xff;
+	return cc;
+}
+
+static inline int __memcpy_fromio_inuser(void __user *dst,
+				     const void __iomem *src,
+				     unsigned long n)
+{
+	int size, rc = 0;
+	u8 status;
+	mm_segment_t old_fs;
+
+	old_fs = enable_sacf_uaccess();
+	while (n > 0) {
+		size = zpci_get_max_write_size((u64 __force) src,
+					       (u64 __force) dst, n,
+					       ZPCI_MAX_READ_SIZE);
+		rc = __pcilg_mio_inuser(dst, src, size, &status);
+		if (rc)
+			break;
+		src += size;
+		dst += size;
+		n -= size;
+	}
+	disable_sacf_uaccess(old_fs);
+	if (rc)
+		zpci_err_mmio(rc, status, (__force u64) dst);
+	return rc;
+}
+
 SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
 		void __user *, user_buffer, size_t, length)
 {
@@ -86,12 +280,27 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsi
 
 	if (length <= 0 || PAGE_SIZE - (mmio_addr & ~PAGE_MASK) < length)
 		return -EINVAL;
+
+	/*
+	 * Only support write access to MIO capable devices on a MIO enabled
+	 * system. Otherwise we would have to check for every address if it is
+	 * a special ZPCI_ADDR and we would have to do a get_pfn() which we
+	 * don't need for MIO capable devices.
+	 */
+	if (static_branch_likely(&have_mio)) {
+		ret = __memcpy_fromio_inuser(
+				user_buffer, (const void __iomem *)mmio_addr,
+				length);
+		return ret;
+	}
+
 	if (length > 64) {
 		buf = kmalloc(length, GFP_KERNEL);
 		if (!buf)
 			return -ENOMEM;
-	} else
+	} else {
 		buf = local_buf;
+	}
 
 	ret = get_pfn(mmio_addr, VM_READ, &pfn);
 	if (ret)


