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Subject[PATCH v9 12/17] platform/x86: dell-smbios: Add filtering support
Date
When a userspace interface is introduced to dell-smbios filtering
support will be used to make sure that userspace doesn't make calls
deemed unsafe or that can cause the kernel drivers to get out of
sync.

A blacklist is provided for the following:
- Items that are in use by other kernel drivers
- Items that are deemed unsafe (diagnostics, write-once, etc)
- Any items in the blacklist will be rejected.

Following that a whitelist is provided as follows:
- Each item has an associated capability. If a userspace interface
accesses this item, that capability will be tested to filter
the request.
- If the process provides CAP_SYS_RAWIO the whitelist will be
overridden.

When an item is not in the blacklist, or whitelist and the process
is run with insufficient capabilities the call will be rejected.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
---
drivers/platform/x86/dell-smbios.c | 190 +++++++++++++++++++++++++++++++++++++
drivers/platform/x86/dell-smbios.h | 11 +++
2 files changed, 201 insertions(+)

diff --git a/drivers/platform/x86/dell-smbios.c b/drivers/platform/x86/dell-smbios.c
index b540cd4605f7..b2aeb740c04b 100644
--- a/drivers/platform/x86/dell-smbios.c
+++ b/drivers/platform/x86/dell-smbios.c
@@ -24,6 +24,7 @@
#include <linux/slab.h>
#include "dell-smbios.h"

+static u32 da_supported_commands;
static int da_num_tokens;
static struct platform_device *platform_device;
static struct calling_interface_token *da_tokens;
@@ -38,6 +39,91 @@ struct smbios_device {
int (*call_fn)(struct calling_interface_buffer *);
};

+struct smbios_call {
+ u32 need_capability;
+ int class;
+ int select;
+};
+
+/* calls that are whitelisted for given capabilities */
+static struct smbios_call call_whitelist[] = {
+ /* generally tokens are allowed, but may be further filtered or
+ * restricted by token blacklist or whitelist
+ */
+ {CAP_SYS_ADMIN, CLASS_TOKEN_READ, SELECT_TOKEN_STD},
+ {CAP_SYS_ADMIN, CLASS_TOKEN_READ, SELECT_TOKEN_AC},
+ {CAP_SYS_ADMIN, CLASS_TOKEN_READ, SELECT_TOKEN_BAT},
+ {CAP_SYS_ADMIN, CLASS_TOKEN_WRITE, SELECT_TOKEN_STD},
+ {CAP_SYS_ADMIN, CLASS_TOKEN_WRITE, SELECT_TOKEN_AC},
+ {CAP_SYS_ADMIN, CLASS_TOKEN_WRITE, SELECT_TOKEN_BAT},
+ /* used by userspace: fwupdate */
+ {CAP_SYS_ADMIN, CLASS_ADMIN_PROP, SELECT_ADMIN_PROP},
+ /* used by userspace: fwupd */
+ {CAP_SYS_ADMIN, CLASS_INFO, SELECT_DOCK},
+ {CAP_SYS_ADMIN, CLASS_FLASH_INTERFACE, SELECT_FLASH_INTERFACE},
+};
+
+/* calls that are explicitly blacklisted */
+static struct smbios_call call_blacklist[] = {
+ {0x0000, 01, 07}, /* manufacturing use */
+ {0x0000, 06, 05}, /* manufacturing use */
+ {0x0000, 11, 03}, /* write once */
+ {0x0000, 11, 07}, /* write once */
+ {0x0000, 11, 11}, /* write once */
+ {0x0000, 19, -1}, /* diagnostics */
+ /* handled by kernel: dell-laptop */
+ {0x0000, CLASS_INFO, SELECT_RFKILL},
+ {0x0000, CLASS_KBD_BACKLIGHT, SELECT_KBD_BACKLIGHT},
+};
+
+struct token_range {
+ u32 need_capability;
+ u16 min;
+ u16 max;
+};
+
+/* tokens that are whitelisted for given capabilities */
+static struct token_range token_whitelist[] = {
+ /* used by userspace: fwupdate */
+ {CAP_SYS_ADMIN, CAPSULE_EN_TOKEN, CAPSULE_DIS_TOKEN},
+ /* can indicate to userspace that WMI is needed */
+ {0x0000, WSMT_EN_TOKEN, WSMT_DIS_TOKEN}
+};
+
+/* tokens that are explicitly blacklisted */
+static struct token_range token_blacklist[] = {
+ {0x0000, 0x0058, 0x0059}, /* ME use */
+ {0x0000, 0x00CD, 0x00D0}, /* raid shadow copy */
+ {0x0000, 0x013A, 0x01FF}, /* sata shadow copy */
+ {0x0000, 0x0175, 0x0176}, /* write once */
+ {0x0000, 0x0195, 0x0197}, /* diagnostics */
+ {0x0000, 0x01DC, 0x01DD}, /* manufacturing use */
+ {0x0000, 0x027D, 0x0284}, /* diagnostics */
+ {0x0000, 0x02E3, 0x02E3}, /* manufacturing use */
+ {0x0000, 0x02FF, 0x02FF}, /* manufacturing use */
+ {0x0000, 0x0300, 0x0302}, /* manufacturing use */
+ {0x0000, 0x0325, 0x0326}, /* manufacturing use */
+ {0x0000, 0x0332, 0x0335}, /* fan control */
+ {0x0000, 0x0350, 0x0350}, /* manufacturing use */
+ {0x0000, 0x0363, 0x0363}, /* manufacturing use */
+ {0x0000, 0x0368, 0x0368}, /* manufacturing use */
+ {0x0000, 0x03F6, 0x03F7}, /* manufacturing use */
+ {0x0000, 0x049E, 0x049F}, /* manufacturing use */
+ {0x0000, 0x04A0, 0x04A3}, /* disagnostics */
+ {0x0000, 0x04E6, 0x04E7}, /* manufacturing use */
+ {0x0000, 0x4000, 0x7FFF}, /* internal BIOS use */
+ {0x0000, 0x9000, 0x9001}, /* internal BIOS use */
+ {0x0000, 0xA000, 0xBFFF}, /* write only */
+ {0x0000, 0xEFF0, 0xEFFF}, /* internal BIOS use */
+ /* handled by kernel: dell-laptop */
+ {0x0000, BRIGHTNESS_TOKEN, BRIGHTNESS_TOKEN},
+ {0x0000, KBD_LED_OFF_TOKEN, KBD_LED_AUTO_TOKEN},
+ {0x0000, KBD_LED_AC_TOKEN, KBD_LED_AC_TOKEN},
+ {0x0000, KBD_LED_AUTO_25_TOKEN, KBD_LED_AUTO_75_TOKEN},
+ {0x0000, KBD_LED_AUTO_100_TOKEN, KBD_LED_AUTO_100_TOKEN},
+ {0x0000, GLOBAL_MIC_MUTE_ENABLE, GLOBAL_MIC_MUTE_DISABLE},
+};
+
static LIST_HEAD(smbios_device_list);

int dell_smbios_error(int value)
@@ -90,6 +176,108 @@ void dell_smbios_unregister_device(struct device *d)
}
EXPORT_SYMBOL_GPL(dell_smbios_unregister_device);

+int dell_smbios_call_filter(struct device *d,
+ struct calling_interface_buffer *buffer)
+{
+ u16 t = 0;
+ int i;
+
+ /* can't make calls over 30 */
+ if (buffer->class > 30) {
+ dev_dbg(d, "class too big: %u\n", buffer->class);
+ return -EINVAL;
+ }
+
+ /* supported calls on the particular system */
+ if (!(da_supported_commands & (1 << buffer->class))) {
+ dev_dbg(d, "invalid command, supported commands: 0x%8x\n",
+ da_supported_commands);
+ return -EINVAL;
+ }
+
+ /* match against call blacklist */
+ for (i = 0; i < ARRAY_SIZE(call_blacklist); i++) {
+ if (buffer->class != call_blacklist[i].class)
+ continue;
+ if (buffer->select != call_blacklist[i].select &&
+ call_blacklist[i].select != -1)
+ continue;
+ dev_dbg(d, "blacklisted command: %u/%u\n",
+ buffer->class, buffer->select);
+ return -EINVAL;
+ }
+
+ /* if a token call, find token ID */
+ if ((buffer->class == CLASS_TOKEN_READ && buffer->select < 3) ||
+ (buffer->class == CLASS_TOKEN_WRITE && buffer->select < 3)) {
+ /* find the matching token ID */
+ for (i = 0; i < da_num_tokens; i++) {
+ if (da_tokens[i].location != buffer->input[0])
+ continue;
+ t = da_tokens[i].tokenID;
+ break;
+ }
+
+ /* token call; but token didn't exist */
+ if (!t) {
+ dev_dbg(d, "token at location %04x doesn't exist\n",
+ buffer->input[0]);
+ return -EINVAL;
+ }
+
+ /* match against token blacklist */
+ for (i = 0; i < ARRAY_SIZE(token_blacklist); i++) {
+ if (!token_blacklist[i].min || !token_blacklist[i].max)
+ continue;
+ if (t >= token_blacklist[i].min &&
+ t <= token_blacklist[i].max)
+ return -EINVAL;
+ }
+
+ /* match against token whitelist */
+ for (i = 0; i < ARRAY_SIZE(token_whitelist); i++) {
+ if (!token_whitelist[i].min || !token_whitelist[i].max)
+ continue;
+ if (t < token_whitelist[i].min ||
+ t > token_whitelist[i].max)
+ continue;
+ if (!token_whitelist[i].need_capability ||
+ capable(token_whitelist[i].need_capability)) {
+ dev_dbg(d, "whitelisted token: %x\n", t);
+ return 0;
+ }
+
+ }
+ }
+ /* match against call whitelist */
+ for (i = 0; i < ARRAY_SIZE(call_whitelist); i++) {
+ if (buffer->class != call_whitelist[i].class)
+ continue;
+ if (buffer->select != call_whitelist[i].select)
+ continue;
+ if (!call_whitelist[i].need_capability ||
+ capable(call_whitelist[i].need_capability)) {
+ dev_dbg(d, "whitelisted capable command: %u/%u\n",
+ buffer->class, buffer->select);
+ return 0;
+ }
+ dev_dbg(d, "missing capability %d for %u/%u\n",
+ call_whitelist[i].need_capability,
+ buffer->class, buffer->select);
+
+ }
+
+ /* not in a whitelist, only allow processes with capabilities */
+ if (capable(CAP_SYS_RAWIO)) {
+ dev_dbg(d, "Allowing %u/%u due to CAP_SYS_RAWIO\n",
+ buffer->class, buffer->select);
+ return 0;
+ }
+
+ return -EACCES;
+}
+EXPORT_SYMBOL_GPL(dell_smbios_call_filter);
+
int dell_smbios_call(struct calling_interface_buffer *buffer)
{
int (*call_fn)(struct calling_interface_buffer *) = NULL;
@@ -168,6 +356,8 @@ static void __init parse_da_table(const struct dmi_header *dm)
if (dm->length < 17)
return;

+ da_supported_commands = table->supportedCmds;
+
new_da_tokens = krealloc(da_tokens, (da_num_tokens + tokens) *
sizeof(struct calling_interface_token),
GFP_KERNEL);
diff --git a/drivers/platform/x86/dell-smbios.h b/drivers/platform/x86/dell-smbios.h
index db6a16e5f87c..91b9c615452d 100644
--- a/drivers/platform/x86/dell-smbios.h
+++ b/drivers/platform/x86/dell-smbios.h
@@ -26,9 +26,14 @@
#define SELECT_TOKEN_AC 2
#define CLASS_KBD_BACKLIGHT 4
#define SELECT_KBD_BACKLIGHT 11
+#define CLASS_FLASH_INTERFACE 7
+#define SELECT_FLASH_INTERFACE 3
+#define CLASS_ADMIN_PROP 10
+#define SELECT_ADMIN_PROP 3
#define CLASS_INFO 17
#define SELECT_RFKILL 11
#define SELECT_APP_REGISTRATION 3
+#define SELECT_DOCK 22

/* Tokens used in kernel drivers, any of these
* should be filtered from userspace access
@@ -44,6 +49,10 @@
#define KBD_LED_AUTO_100_TOKEN 0x02F6
#define GLOBAL_MIC_MUTE_ENABLE 0x0364
#define GLOBAL_MIC_MUTE_DISABLE 0x0365
+
+/* tokens whitelisted to userspace use */
+#define CAPSULE_EN_TOKEN 0x0461
+#define CAPSULE_DIS_TOKEN 0x0462
#define WSMT_EN_TOKEN 0x04EC
#define WSMT_DIS_TOKEN 0x04ED

@@ -80,6 +89,8 @@ int dell_smbios_register_device(struct device *d, void *call_fn);
void dell_smbios_unregister_device(struct device *d);

int dell_smbios_error(int value);
+int dell_smbios_call_filter(struct device *d,
+ struct calling_interface_buffer *buffer);
int dell_smbios_call(struct calling_interface_buffer *buffer);

struct calling_interface_token *dell_smbios_find_token(int tokenid);
--
2.14.1
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