Re: [PATCH][V2] ACPI: sysfs: copy ACPI data using io memory copying

[Mark Rutland <mark.rutland@arm.com>]

[adding James and Lorenzo]

On Tue, Mar 17, 2020 at 04:54:09PM +0000, Colin King wrote:
> 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.

Just to check, is that correct is it correct to map those tables with
Device attributes in the first place, or should we be mapping the tables
with Normal Cacheable attributes with memremap()?

If the FW placed those into memory using cacheavble attributes, reading
them using Device attributes could result in stale values, which could
be garbage.

Thanks,
Mark.

> 
> 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
>