Hi André,
On Mon, Oct 21, 2024 at 01:37:24PM -0300, André Almeida wrote:
> Expose filesystem features through sysfs, so userspace can query if
> tmpfs support casefold.
>
> This follows the same setup as defined by ext4 and f2fs to expose
> casefold support to userspace.
>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> Reviewed-by: Gabriel Krisman Bertazi <krisman@xxxxxxx>
> ---
> mm/shmem.c | 37 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 37 insertions(+)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ea01628e443423d82d44277e085b867ab9bf4b28..0739143d1419c732359d3a3c3457c3acb90c5b22 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5546,3 +5546,40 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
> return page;
> }
> EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
> +
> +#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
> +#if IS_ENABLED(CONFIG_UNICODE)
> +static DEVICE_STRING_ATTR_RO(casefold, 0444, "supported");
> +#endif
> +
> +static struct attribute *tmpfs_attributes[] = {
> +#if IS_ENABLED(CONFIG_UNICODE)
> + &dev_attr_casefold.attr.attr,
> +#endif
> + NULL
> +};
> +
> +static const struct attribute_group tmpfs_attribute_group = {
> + .attrs = tmpfs_attributes,
> + .name = "features"
> +};
> +
> +static struct kobject *tmpfs_kobj;
> +
> +static int __init tmpfs_sysfs_init(void)
> +{
> + int ret;
> +
> + tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
> + if (!tmpfs_kobj)
> + return -ENOMEM;
> +
> + ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
> + if (ret)
> + kobject_put(tmpfs_kobj);
> +
> + return ret;
> +}
> +
> +fs_initcall(tmpfs_sysfs_init);
> +#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
>
> --
> 2.47.0
>
This change as commit 5132f08bd332 ("tmpfs: Expose filesystem features
via sysfs") in -next introduces a kCFI violation when accessing
/sys/fs/tmpfs/features/casefold. An attribute group created with
sysfs_create_group() has ->sysfs_ops() set to kobj_sysfs_ops, which has
a ->show() value of kobj_attr_show(). When kobj_attr_show() goes to call
the attribute's ->show() value after container_of(), there will be a
type mismatch in the case of the casefold attr, as it was defined with a
->show() value of device_show_string() but that does not match the type
of ->show() in 'struct kobj_attribute'.
I can easily reproduce this with the following commands:
$ printf 'CONFIG_%s=y\n' CFI_CLANG UNICODE >kernel/configs/repro.config
$ make -skj"$(nproc)" ARCH=arm64 LLVM=1 mrproper virtconfig repro.config Image.gz
...
$ curl -LSs https://github.com/ClangBuiltLinux/boot-utils/releases/download/20230707-182910/arm64-rootfs.cpio.zst | zstd -d >rootfs.cpio
$ qemu-system-aarch64 \
-display none \
-nodefaults \
-cpu max,pauth-impdef=true \
-machine virt,gic-version=max,virtualization=true \
-append 'console=ttyAMA0 earlycon rdinit=/bin/sh' \
-kernel arch/arm64/boot/Image.gz \
-initrd rootfs.cpio \
-m 512m \
-serial mon:stdio
...
# mount -t sysfs sys /sys
# cat /sys/fs/tmpfs/features/casefold
[ 70.558496] CFI failure at kobj_attr_show+0x2c/0x4c (target: device_show_string+0x0/0x38; expected type: 0xc527b809)
[ 70.560018] Internal error: Oops - CFI: 00000000f2008228 [#1] PREEMPT SMP
[ 70.560647] Modules linked in:
[ 70.561770] CPU: 0 UID: 0 PID: 46 Comm: cat Not tainted 6.12.0-rc4-00008-g5132f08bd332 #1
[ 70.562429] Hardware name: linux,dummy-virt (DT)
[ 70.562897] pstate: 21402009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 70.563377] pc : kobj_attr_show+0x2c/0x4c
[ 70.563674] lr : sysfs_kf_seq_show+0xb4/0x130
[ 70.563987] sp : ffff80008043bac0
[ 70.564236] x29: ffff80008043bac0 x28: 000000007ffff001 x27: 0000000000000000
[ 70.564877] x26: 0000000001000000 x25: 000000007ffff001 x24: 0000000000000001
[ 70.565339] x23: fff000000238a000 x22: ffff9fa31a3996f8 x21: fff00000023fc000
[ 70.565806] x20: fff000000201df80 x19: fff000000238b000 x18: 0000000000000000
[ 70.566273] x17: 00000000c527b809 x16: 00000000df43c25c x15: fff000001fef8200
[ 70.566727] x14: 0000000000000000 x13: fff00000022450f0 x12: 0000000000001000
[ 70.567177] x11: fff00000023fc000 x10: 0000000000000000 x9 : ffff9fa31a18fac4
[ 70.567682] x8 : ffff9fa319badde4 x7 : 0000000000000000 x6 : 000000000000003f
[ 70.568138] x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004
[ 70.568585] x2 : fff00000023fc000 x1 : ffff9fa31a881f90 x0 : fff000000201df80
[ 70.569169] Call trace:
[ 70.569389] kobj_attr_show+0x2c/0x4c
[ 70.569706] sysfs_kf_seq_show+0xb4/0x130
[ 70.570020] kernfs_seq_show+0x44/0x54
[ 70.570280] seq_read_iter+0x14c/0x4b0
[ 70.570543] kernfs_fop_read_iter+0x60/0x198
[ 70.570820] copy_splice_read+0x1f0/0x2f4
[ 70.571092] splice_direct_to_actor+0xf4/0x2e0
[ 70.571376] do_splice_direct+0x68/0xb8
[ 70.571626] do_sendfile+0x1e8/0x488
[ 70.571874] __arm64_sys_sendfile64+0xe0/0x12c
[ 70.572161] invoke_syscall+0x58/0x114
[ 70.572424] el0_svc_common+0xa8/0xdc
[ 70.572676] do_el0_svc+0x1c/0x28
[ 70.572910] el0_svc+0x38/0x68
[ 70.573132] el0t_64_sync_handler+0x90/0xfc
[ 70.573394] el0t_64_sync+0x190/0x19
[ 70.574001] Code: 72970131 72b8a4f1 6b11021f 54000040 (d4304500)
[ 70.574635] ---[ end trace 0000000000000000 ]---
I am not sure if there is a better API exists or if a local copy should
be rolled but I think the current scheme is definitely wrong because
there is no 'struct device' here.
If there is any patch I can test or further information I can provide, I
am more than happy to do so.
Cheers,
Nathan
