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From:   Colin King <colin.king@canonical.com>
To:     "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     kernel-janitors@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH][V2] ACPI: sysfs: copy ACPI data using io memory copying
Date:   Tue, 17 Mar 2020 16:54:09 +0000
Message-Id: <20200317165409.469013-1-colin.king@canonical.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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From: Colin Ian King <colin.king@canonical.com>

Reading ACPI data on ARM64 at a non-aligned offset from
/sys/firmware/acpi/tables/data/BERT will cause a splat because
the data is I/O memory mapped and being read with just a memcpy.
Fix this by introducing an I/O variant of memory_read_from_buffer
and using I/O memory mapped copies instead.

Fixes the following splat:

[  439.789355] Unable to handle kernel paging request at virtual address ffff800041ac0007
[  439.797275] Mem abort info:
[  439.800078]   ESR = 0x96000021
[  439.803131]   EC = 0x25: DABT (current EL), IL = 32 bits
[  439.808437]   SET = 0, FnV = 0
[  439.811486]   EA = 0, S1PTW = 0
[  439.814621] Data abort info:
[  439.817489]   ISV = 0, ISS = 0x00000021
[  439.821319]   CM = 0, WnR = 0
[  439.824282] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000817fc000
[  439.830979] [ffff800041ac0007] pgd=000000bffcfff003, pud=0000009f27cee003, pmd=000000bf4b993003, pte=0068000080280703
[  439.841584] Internal error: Oops: 96000021 [#1] SMP
[  439.846449] Modules linked in: nls_iso8859_1 dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua ipmi_ssif input_leds joydev ipmi_devintf ipmi_msghandler thunderx2_pmu sch_fq_codel ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon raid6_pq libcrc32c raid1 raid0 multipath linear i2c_smbus ast i2c_algo_bit crct10dif_ce drm_vram_helper uas ttm ghash_ce drm_kms_helper sha2_ce syscopyarea sha256_arm64 qede sysfillrect mpt3sas sha1_ce sysimgblt fb_sys_fops raid_class qed drm scsi_transport_sas usb_storage ahci crc8 gpio_xlp i2c_xlp9xx hid_generic usbhid hid aes_neon_bs aes_neon_blk aes_ce_blk crypto_simd cryptd aes_ce_cipher
[  439.908474] CPU: 2 PID: 3926 Comm: a.out Not tainted 5.4.0-14-generic #17-Ubuntu
[  439.915855] Hardware name: To be filled by O.E.M. Saber/Saber, BIOS 0ACKL027 07/01/2019
[  439.923844] pstate: 80400009 (Nzcv daif +PAN -UAO)
[  439.928625] pc : __memcpy+0x90/0x180
[  439.932192] lr : memory_read_from_buffer+0x64/0x88
[  439.936968] sp : ffff8000350dbc70
[  439.940270] x29: ffff8000350dbc70 x28: ffff009e9c444b00
[  439.945568] x27: 0000000000000000 x26: 0000000000000000
[  439.950866] x25: 0000000056000000 x24: ffff800041ac0000
[  439.956164] x23: ffff009ea163f980 x22: 0000000000000007
[  439.961462] x21: ffff8000350dbce8 x20: 000000000000000e
[  439.966760] x19: 0000000000000007 x18: ffff8000112f64a8
[  439.972058] x17: 0000000000000000 x16: 0000000000000000
[  439.977355] x15: 0000000080280000 x14: ffff800041aed000
[  439.982653] x13: ffff009ee9fa2840 x12: ffff800041ad1000
[  439.987951] x11: ffff8000115e1360 x10: ffff8000115e1360
[  439.993248] x9 : 0000000000010000 x8 : ffff800011ad2658
[  439.998546] x7 : ffff800041ac0000 x6 : ffff009ea163f980
[  440.003844] x5 : 0140000000000000 x4 : 0000000000010000
[  440.009141] x3 : ffff800041ac0000 x2 : 0000000000000007
[  440.014439] x1 : ffff800041ac0007 x0 : ffff009ea163f980
[  440.019737] Call trace:
[  440.022173]  __memcpy+0x90/0x180
[  440.025392]  acpi_data_show+0x54/0x80
[  440.029044]  sysfs_kf_bin_read+0x6c/0xa8
[  440.032954]  kernfs_file_direct_read+0x90/0x2d0
[  440.037470]  kernfs_fop_read+0x68/0x78
[  440.041210]  __vfs_read+0x48/0x90
[  440.044511]  vfs_read+0xd0/0x1a0
[  440.047726]  ksys_read+0x78/0x100
[  440.051028]  __arm64_sys_read+0x24/0x30
[  440.054852]  el0_svc_common.constprop.0+0xdc/0x1d8
[  440.059629]  el0_svc_handler+0x34/0xa0
[  440.063366]  el0_svc+0x10/0x14
[  440.066411] Code: 36180062 f8408423 f80084c3 36100062 (b8404423)
[  440.072492] ---[ end trace 45fb374e8d2d800e ]---

A simple reproducer is as follows:

int main(void)
{
        int fd;
        char buffer[7];
        ssize_t n;

        fd = open("/sys/firmware/acpi/tables/data/BERT", O_RDONLY);
        if (fd < 0) {
                perror("open failed");
                return -1;
        }
        do {
                n = read(fd, buffer, sizeof(buffer));
        } while (n > 0);

        return 0;
}

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
V2: Add missing #include <linux/io.h> without which we get
    a build failure when building with allnoconfig 
---
 drivers/acpi/sysfs.c   |  2 +-
 fs/libfs.c             | 34 ++++++++++++++++++++++++++++++++++
 include/linux/string.h |  2 ++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
index c60d2c6..fb9e216 100644
--- a/drivers/acpi/sysfs.c
+++ b/drivers/acpi/sysfs.c
@@ -446,7 +446,7 @@ static ssize_t acpi_data_show(struct file *filp, struct kobject *kobj,
 	base = acpi_os_map_memory(data_attr->addr, data_attr->attr.size);
 	if (!base)
 		return -ENOMEM;
-	rc = memory_read_from_buffer(buf, count, &offset, base,
+	rc = memory_read_from_io_buffer(buf, count, &offset, base,
 				     data_attr->attr.size);
 	acpi_os_unmap_memory(base, data_attr->attr.size);
 
diff --git a/fs/libfs.c b/fs/libfs.c
index c686bd9..1a49da1 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -20,6 +20,7 @@
 #include <linux/fs_context.h>
 #include <linux/pseudo_fs.h>
 #include <linux/fsnotify.h>
+#include <linux/io.h>
 
 #include <linux/uaccess.h>
 
@@ -800,6 +801,39 @@ ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
 }
 EXPORT_SYMBOL(memory_read_from_buffer);
 
+/**
+ * memory_read_from_io_buffer - copy data from a io memory mapped buffer
+ * @to: the kernel space buffer to read to
+ * @count: the maximum number of bytes to read
+ * @ppos: the current position in the buffer
+ * @from: the buffer to read from
+ * @available: the size of the buffer
+ *
+ * The memory_read_from_buffer() function reads up to @count bytes from the
+ * io memory mappy buffer @from at offset @ppos into the kernel space address
+ * starting at @to.
+ *
+ * On success, the number of bytes read is returned and the offset @ppos is
+ * advanced by this number, or negative value is returned on error.
+ **/
+ssize_t memory_read_from_io_buffer(void *to, size_t count, loff_t *ppos,
+				   const void *from, size_t available)
+{
+	loff_t pos = *ppos;
+
+	if (pos < 0)
+		return -EINVAL;
+	if (pos >= available)
+		return 0;
+	if (count > available - pos)
+		count = available - pos;
+	memcpy_fromio(to, from + pos, count);
+	*ppos = pos + count;
+
+	return count;
+}
+EXPORT_SYMBOL(memory_read_from_io_buffer);
+
 /*
  * Transaction based IO.
  * The file expects a single write which triggers the transaction, and then
diff --git a/include/linux/string.h b/include/linux/string.h
index 6dfbb2e..0c6ec2a 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -216,6 +216,8 @@ int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
 
 extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
 				       const void *from, size_t available);
+extern ssize_t memory_read_from_io_buffer(void *to, size_t count, loff_t *ppos,
+					  const void *from, size_t available);
 
 int ptr_to_hashval(const void *ptr, unsigned long *hashval_out);
 
-- 
2.7.4