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Date: Wed, 13 Jan 2016 14:28:18 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Pali Rohár <pali.rohar@...il.com>,
Jean Delvare <jdelvare@...e.com>
Cc: Andy Lutomirski <luto@...nel.org>,
platform-driver-x86@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
stable <stable@...r.kernel.org>
Subject: Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables
[cc: Jean Delvare]
On Tue, Jan 12, 2016 at 6:25 AM, Pali Rohár <pali.rohar@...il.com> wrote:
> On Monday 11 January 2016 13:58:20 Andy Lutomirski wrote:
>> On Sun, Jan 3, 2016 at 6:52 AM, Andy Lutomirski <luto@...nel.org> wrote:
>> > The dmi_walk function maps the DMI table, walks it, and unmaps it.
>> > This means that the dell_bios_hotkey_table that find_hk_type stores
>> > points to unmapped memory by the time it gets read.
>> >
>> > I've been able to trigger crashes caused by the stale pointer a
>> > couple of times, but never on a stock kernel.
>> >
>> > Fix it by generating the keymap in the dmi_walk callback instead of
>> > storing a pointer.
>>
>> Quick ping: has anyone had a chance to look at this?
>>
>> --Andy
>>
>
> Hi Andy, I looked at this patch, but I think some people from -mm or DMI
> code should look at it as it is memory problem... We also has one in
> dell-laptop.ko (wrong API usage) and so -mm people could know it better.
Let's ask:
Jean, am I right that drivers must not store pointers to DMI tables
that they find through dmi_walk? Is there any alternative interface
that could be used to get a longer-lived pointer to DMI tables, or
should drivers just parse them and copy out any info needed from the
dmi_walk callback?
There are at least two platform drivers (dell-wmi and dell-laptop)
that don't play well with the current interface. This patch is
intended to fix one of them.
--Andy
>
>> >
>> > Cc: stable@...r.kernel.org
>> > Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> > ---
>> >
>> > This seems to work on my laptop. It applies to platform-drivers-x86/for-next.
>> >
>> > drivers/platform/x86/dell-wmi.c | 69 +++++++++++++++++++++++++----------------
>> > 1 file changed, 42 insertions(+), 27 deletions(-)
>> >
>> > diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
>> > index 57402c4c394e..52db2721d7e3 100644
>> > --- a/drivers/platform/x86/dell-wmi.c
>> > +++ b/drivers/platform/x86/dell-wmi.c
>> > @@ -116,7 +116,10 @@ struct dell_bios_hotkey_table {
>> >
>> > };
>> >
>> > -static const struct dell_bios_hotkey_table *dell_bios_hotkey_table;
>> > +struct dell_dmi_results {
>> > + int err;
>> > + struct key_entry *keymap;
>> > +};
>> >
>> > /* Uninitialized entries here are KEY_RESERVED == 0. */
>> > static const u16 bios_to_linux_keycode[256] __initconst = {
>> > @@ -316,20 +319,34 @@ static void dell_wmi_notify(u32 value, void *context)
>> > kfree(obj);
>> > }
>> >
>> > -static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
>> > +static void __init handle_dmi_table(const struct dmi_header *dm,
>> > + void *opaque)
>> > {
>> > - int hotkey_num = (dell_bios_hotkey_table->header.length - 4) /
>> > - sizeof(struct dell_bios_keymap_entry);
>> > + struct dell_dmi_results *results = opaque;
>> > + struct dell_bios_hotkey_table *table;
>> > struct key_entry *keymap;
>> > - int i;
>> > + int hotkey_num, i;
>> > +
>> > + if (results->err || results->keymap)
>> > + return; /* We already found the hotkey table. */
>> > +
>> > + if (dm->type != 0xb2 || dm->length <= 6)
>> > + return;
>> > +
>> > + table = container_of(dm, struct dell_bios_hotkey_table, header);
>> > +
>> > + hotkey_num = (table->header.length - 4) /
>> > + sizeof(struct dell_bios_keymap_entry);
>> >
>> > keymap = kcalloc(hotkey_num + 1, sizeof(struct key_entry), GFP_KERNEL);
>> > - if (!keymap)
>> > - return NULL;
>> > + if (!keymap) {
>> > + results->err = -ENOMEM;
>> > + return;
>> > + }
>> >
>> > for (i = 0; i < hotkey_num; i++) {
>> > const struct dell_bios_keymap_entry *bios_entry =
>> > - &dell_bios_hotkey_table->keymap[i];
>> > + &table->keymap[i];
>> >
>> > /* Uninitialized entries are 0 aka KEY_RESERVED. */
>> > u16 keycode = (bios_entry->keycode <
>> > @@ -358,11 +375,13 @@ static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
>> >
>> > keymap[hotkey_num].type = KE_END;
>> >
>> > - return keymap;
>> > + results->err = 0;
>> > + results->keymap = keymap;
>> > }
>> >
>> > static int __init dell_wmi_input_setup(void)
>> > {
>> > + struct dell_dmi_results dmi_results = {};
>> > int err;
>> >
>> > dell_wmi_input_dev = input_allocate_device();
>> > @@ -373,20 +392,26 @@ static int __init dell_wmi_input_setup(void)
>> > dell_wmi_input_dev->phys = "wmi/input0";
>> > dell_wmi_input_dev->id.bustype = BUS_HOST;
>> >
>> > - if (dell_new_hk_type) {
>> > - const struct key_entry *keymap = dell_wmi_prepare_new_keymap();
>> > - if (!keymap) {
>> > - err = -ENOMEM;
>> > - goto err_free_dev;
>> > - }
>> > + err = dmi_walk(handle_dmi_table, &dmi_results);
>> > + if (err)
>> > + goto err_free_dev;
>> >
>> > - err = sparse_keymap_setup(dell_wmi_input_dev, keymap, NULL);
>> > + if (dmi_results.err) {
>> > + err = dmi_results.err;
>> > + goto err_free_dev;
>> > + }
>> > +
>> > + if (dmi_results.keymap) {
>> > + dell_new_hk_type = true;
>> > +
>> > + err = sparse_keymap_setup(dell_wmi_input_dev,
>> > + dmi_results.keymap, NULL);
>> >
>> > /*
>> > * Sparse keymap library makes a copy of keymap so we
>> > * don't need the original one that was allocated.
>> > */
>> > - kfree(keymap);
>> > + kfree(dmi_results.keymap);
>> > } else {
>> > err = sparse_keymap_setup(dell_wmi_input_dev,
>> > dell_wmi_legacy_keymap, NULL);
>> > @@ -413,15 +438,6 @@ static void dell_wmi_input_destroy(void)
>> > input_unregister_device(dell_wmi_input_dev);
>> > }
>> >
>> > -static void __init find_hk_type(const struct dmi_header *dm, void *dummy)
>> > -{
>> > - if (dm->type == 0xb2 && dm->length > 6) {
>> > - dell_new_hk_type = true;
>> > - dell_bios_hotkey_table =
>> > - container_of(dm, struct dell_bios_hotkey_table, header);
>> > - }
>> > -}
>> > -
>> > static int __init dell_wmi_init(void)
>> > {
>> > int err;
>> > @@ -432,7 +448,6 @@ static int __init dell_wmi_init(void)
>> > return -ENODEV;
>> > }
>> >
>> > - dmi_walk(find_hk_type, NULL);
>> > acpi_video = acpi_video_get_backlight_type() != acpi_backlight_vendor;
>> >
>> > err = dell_wmi_input_setup();
>> > --
>> > 2.5.0
>> >
>>
>>
>>
>
> --
> Pali Rohár
> pali.rohar@...il.com
--
Andy Lutomirski
AMA Capital Management, LLC
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