Messages in this thread | | | Date | Tue, 23 May 2023 12:46:07 +0200 | Subject | Re: [PATCH 1/4] platform/x86: think-lmi: Enable opcode support on BIOS settings | From | Hans de Goede <> |
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Hi Mark,
On 5/17/23 20:19, Mark Pearson wrote: > Whilst reviewing some documentation from the FW team on using WMI on > Lenovo system I noticed that we weren't using Opcode support when > changing BIOS settings in the thinkLMI driver. > > We should be doing this to ensure we're future proof as the old > non-opcode mechanism has been deprecated. > > Tested on X1 Carbon G10 and G11. > > Signed-off-by: Mark Pearson <mpearson-lenovo@squebb.ca> > --- > drivers/platform/x86/think-lmi.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/drivers/platform/x86/think-lmi.c b/drivers/platform/x86/think-lmi.c > index 1138f770149d..d9341305eba9 100644 > --- a/drivers/platform/x86/think-lmi.c > +++ b/drivers/platform/x86/think-lmi.c > @@ -1001,7 +1001,28 @@ static ssize_t current_value_store(struct kobject *kobj, > tlmi_priv.pwd_admin->save_signature); > if (ret) > goto out;
> - } else { /* Non certiifcate based authentication */ > + } else if (tlmi_priv.opcode_support) { > + /* If opcode support is present use that interface */ > + set_str = kasprintf(GFP_KERNEL, "%s,%s;", setting->display_name, > + new_setting); > + if (!set_str) { > + ret = -ENOMEM; > + goto out; > + } > + > + ret = tlmi_simple_call(LENOVO_SET_BIOS_SETTINGS_GUID, set_str); > + if (ret) > + goto out; > + > + if (tlmi_priv.pwd_admin->valid && tlmi_priv.pwd_admin->password[0]) { > + ret = tlmi_opcode_setting("WmiOpcodePasswordAdmin", > + tlmi_priv.pwd_admin->password); > + if (ret) > + goto out; > + } > + > + ret = tlmi_save_bios_settings("");
I'm a bit confused about how this works. You are calling the same LENOVO_SET_BIOS_SETTINGS_GUID as the old non opcode based authentication method without any auth string.
And then afterwards you are calling LENOVO_OPCODE_IF_GUID with "WmiOpcodePasswordAdmin:<passwd>"
Won't the initial LENOVO_SET_BIOS_SETTINGS_GUID get rejected since it does not include an auth-string and you have not authenticated yet using the opcode mechanism either. IOW shouldn't the opcode auth call go first ?
And how does this work timing wise, vs races with userspace doing multiple sysfs writes at once.
If the authentication done afterwards really acks the last LENOVO_SET_BIOS_SETTINGS_GUID call then a userspace based attacker could try to race and overwrite the last LENOVO_SET_BIOS_SETTINGS_GUID call before the ack happens... ?
If this code really is correct I think we need to introduce a mutex to avoid this race.
And this also needs some comments to explain what is going on.
Regards,
Hans
> + } else { /* old non opcode based authentication method (deprecated)*/ > if (tlmi_priv.pwd_admin->valid && tlmi_priv.pwd_admin->password[0]) { > auth_str = kasprintf(GFP_KERNEL, "%s,%s,%s;", > tlmi_priv.pwd_admin->password,
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