Re: [PATCH] remoteproc: qcom: Don't memcpy_toio more than is provided

Doug Anderson
2021-12-07T00:01:46Z

Hi,

On Tue, Nov 16, 2021 at 10:55 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> If the string passed into qcom_pil_info_store() isn't as long as
> PIL_RELOC_NAME_LEN we'll try to copy the string assuming the length is
> PIL_RELOC_NAME_LEN to the io space and go beyond the bounds of the
> string. Let's only copy as many byes as the string is long, ignoring the
> NUL terminator.
>
> This fixes the following KASAN error:
>
> BUG: KASAN: global-out-of-bounds in __memcpy_toio+0x124/0x140
> Read of size 1 at addr ffffffd35086e386 by task rmtfs/2392
>
> CPU: 2 PID: 2392 Comm: rmtfs Tainted: G W 5.16.0-rc1-lockdep+ #10
> Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
> Call trace:
> dump_backtrace+0x0/0x410
> show_stack+0x24/0x30
> dump_stack_lvl+0x7c/0xa0
> print_address_description+0x78/0x2bc
> kasan_report+0x160/0x1a0
> __asan_report_load1_noabort+0x44/0x50
> __memcpy_toio+0x124/0x140
> qcom_pil_info_store+0x298/0x358 [qcom_pil_info]
> q6v5_start+0xdf0/0x12e0 [qcom_q6v5_mss]
> rproc_start+0x178/0x3a0
> rproc_boot+0x5f0/0xb90
> state_store+0x78/0x1bc
> dev_attr_store+0x70/0x90
> sysfs_kf_write+0xf4/0x118
> kernfs_fop_write_iter+0x208/0x300
> vfs_write+0x55c/0x804
> ksys_pwrite64+0xc8/0x134
> __arm64_compat_sys_aarch32_pwrite64+0xc4/0xdc
> invoke_syscall+0x78/0x20c
> el0_svc_common+0x11c/0x1f0
> do_el0_svc_compat+0x50/0x60
> el0_svc_compat+0x5c/0xec
> el0t_32_sync_handler+0xc0/0xf0
> el0t_32_sync+0x1a4/0x1a8
>
> The buggy address belongs to the variable:
> .str.59+0x6/0xffffffffffffec80 [qcom_q6v5_mss]
>
> Memory state around the buggy address:
> ffffffd35086e280: 00 00 00 00 02 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
> ffffffd35086e300: 00 02 f9 f9 f9 f9 f9 f9 00 00 00 06 f9 f9 f9 f9
> >ffffffd35086e380: 06 f9 f9 f9 05 f9 f9 f9 00 00 00 00 00 06 f9 f9
> ^
> ffffffd35086e400: f9 f9 f9 f9 01 f9 f9 f9 04 f9 f9 f9 00 00 01 f9
> ffffffd35086e480: f9 f9 f9 f9 00 00 00 00 00 00 00 01 f9 f9 f9 f9
>
> Fixes: 549b67da660d ("remoteproc: qcom: Introduce helper to store pil info in IMEM")
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
> drivers/remoteproc/qcom_pil_info.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/remoteproc/qcom_pil_info.c b/drivers/remoteproc/qcom_pil_info.c
> index 7c007dd7b200..aca21560e20b 100644
> --- a/drivers/remoteproc/qcom_pil_info.c
> +++ b/drivers/remoteproc/qcom_pil_info.c
> @@ -104,7 +104,7 @@ int qcom_pil_info_store(const char *image, phys_addr_t base, size_t size)
> return -ENOMEM;
>
> found_unused:
> - memcpy_toio(entry, image, PIL_RELOC_NAME_LEN);
> + memcpy_toio(entry, image, strnlen(image, PIL_RELOC_NAME_LEN));

The above seems slightly sketchy...

Let's say:

image = "modem" (5 characters plus null termination)
PIL_RELOC_NAME_LEN = 8

...so strnlen(image, 8) = 5, right?
...so we'll copy characters _not_ including the NULL termination.

I guess that's OK as long as we're certain that the destination was
zero-initted, but maybe it would be better/safer to write:

memcpy_toio(entry, image, strnlen(image, PIL_RELOC_NAME_LEN - 1) + 1);

-Doug