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ExynosModemIsolation » History » Version 9

Denis 'GNUtoo' Carikli, 03/02/2020 10:59 AM
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1 9 Denis 'GNUtoo' Carikli
h1. Exynos 3110 modem isolation
2 1 Paul Kocialkowski
3 7 Denis 'GNUtoo' Carikli
This article talks about a very serious freedom, privacy and security issue we found during Replicant development.
4 1 Paul Kocialkowski
5 9 Denis 'GNUtoo' Carikli
We found that the modem wasn't isolated and was potentially able to read and write part of the RAM used by Replicant on several devices with an Exynos 3110.
6 7 Denis 'GNUtoo' Carikli
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h2. Affected devices:
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* Nexus S (GT-I9020)
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* Nexus S (GT-I9020A)
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* Nexus S (GT-I9023)
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13 1 Paul Kocialkowski
h2. Hardware design matrix
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|_. *Chip* |_. Controlled by the CPU |_. Controlled by the modem |_. Connected to the modem |
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| GPS | Yes | No | No? |
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| Audio CODEC | Yes | No | Yes |
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| NAND | Yes | No | No |
19 3 Paul Kocialkowski
| RAM | Yes | Yes (96Mib at least) | Yes |
20 1 Paul Kocialkowski
| WiFi/Bluetooth | Yes | No | No |
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| Sensors | Yes | No | No |
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| NFC | Yes | No | No |
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| Camera | Yes | No | No |
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25 5 Denis 'GNUtoo' Carikli
h2. Modem isolation
26 1 Paul Kocialkowski
27 5 Denis 'GNUtoo' Carikli
The modem (XMM 6160) is separated from the SoC and communicates with it via serial over 16Mib of shared memory: this is bad since it means that RAM is compromised (at least 80Mib + 16Mib = 96Mib) and can be used to spy.
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Regarding audio, the modem is connected to the CODEC but cannot control it (the SoC has to enable routing from/to the modem).
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There is no evidence that the GPS is connected to the modem, but since we cannot check on the hardware, there is no proof it's not connected to it either. The SoC is able to control the GPS power though, so we can keep it off.
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Since the SoC has to load the modem firmware over the (fake) serial, and following the datasheets, the modem is not connected to the NAND.
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32 3 Paul Kocialkowski
The modem is able to spy on (at least) 96 Mib of the main memory. So far, we cannot tell:
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* if it can only spy 80Mib or the full memory
34 1 Paul Kocialkowski
* if it can be fixed or not
35 4 Paul Kocialkowski
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The Linux kernel is being loaded at the beginning of the shared memory bank (0x30000000), however the kernel should be off when it loads.
37 1 Paul Kocialkowski
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h3. Kernel details
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40 5 Denis 'GNUtoo' Carikli
In "kernel-crespo/arch/arm/mach-s5pv210/dev-herring-phone.c":https://git.replicant.us/replicant/kernel_samsung_crespo/tree/arch/arm/mach-s5pv210/dev-herring-phone.c#n49 we have:
41 1 Paul Kocialkowski
<pre>
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static struct resource mdmctl_res[] = {
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[...]
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        [2] = {
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                .name = "onedram",
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                .start = (S5PV210_PA_SDRAM + 0x05000000),
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                .end = (S5PV210_PA_SDRAM + 0x05000000 + SZ_16M - 1),
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                .flags = IORESOURCE_MEM,
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        },
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};
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</pre>
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* S5PV210_PA_SDRAM is 0x30000000
54 3 Paul Kocialkowski
* 0x05000000 is 80Mib
55 1 Paul Kocialkowski
* mdmctl_res goes in a platform device struct which is passed to the modem driver:
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<pre>
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static struct platform_device modemctl = {
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        .name = "modemctl",
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        .id = -1,
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        .num_resources = ARRAY_SIZE(mdmctl_res),
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        .resource = mdmctl_res,
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        .dev = {
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                .platform_data = &mdmctl_data,
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        },
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};
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</pre>
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69 6 Denis 'GNUtoo' Carikli
And in the board file, in "kernel-crespo/arch/arm/mach-s5pv210/mach-herring.c":https://git.replicant.us/replicant/kernel_samsung_crespo/tree/arch/arm/mach-s5pv210/mach-herring.c#n5596 we have: 
70 1 Paul Kocialkowski
<pre>
71
static void __init herring_fixup(struct machine_desc *desc,
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                struct tag *tags, char **cmdline,
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                struct meminfo *mi)
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{
75
        mi->bank[0].start = 0x30000000;
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        mi->bank[0].size = 80 * SZ_1M;
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        mi->bank[0].node = 0;
78
</pre>
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80 3 Paul Kocialkowski
So we can suppose that there is at least one ram chip that is shared between the modem and the main CPU. Avoiding the use of this memory bank would result in loosing 80Mib of memory.
81 4 Paul Kocialkowski
82 8 Denis 'GNUtoo' Carikli
h3. Workaround attempt
83 1 Paul Kocialkowski
84 8 Denis 'GNUtoo' Carikli
It might be possible to limit the amount of damage by relying on the fact that the modem has to be booted by Replicant, and make sure that the RAM chip that is shared with the modem isn't used for other things than this memory sharing.
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This would make us lose about 80Mib of RAM, and the shared memory would still be used for SoC/Modem communication but as the RAM chip would be used only for that, so the modem would not be able read and write problematic data on it.
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We would also need to make sure that the booloader doesn't load the kernel in that region or that the kernel is relocated to some other region before intializing the modem.
89 4 Paul Kocialkowski
90
The current diff with the Nexus S kernel is here, but it doesn't boot at all with the following changes (and mkbootimg changes):
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<pre>
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diff --git a/arch/arm/configs/herring_defconfig b/arch/arm/configs/herring_defconfig
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old mode 100755
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new mode 100644
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index 11abbf0..99bf3f5
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--- a/arch/arm/configs/herring_defconfig
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+++ b/arch/arm/configs/herring_defconfig
99
@@ -1,7 +1,7 @@
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 #
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 # Automatically generated make config: don't edit
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 # Linux kernel version: 2.6.35.7
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-# Fri Jun  3 07:07:08 2011
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+# Sun Apr  8 14:40:16 2012
105
 #
106
 CONFIG_ARM=y
107
 CONFIG_HAVE_PWM=y
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@@ -418,8 +418,8 @@ CONFIG_ALIGNMENT_TRAP=y
109
 #
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 CONFIG_ZBOOT_ROM_TEXT=0
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 CONFIG_ZBOOT_ROM_BSS=0
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-CONFIG_CMDLINE="console=ttyFIQ0"
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-# CONFIG_CMDLINE_FORCE is not set
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+CONFIG_CMDLINE="console=ttyFIQ0 no_console_suspend earlyprintk=serial,ttySAC2,115200 androidboot.serialno=3733BAB66DE200EC androidboot.bootloader=I9020XXKA3 androidboot.baseband=I9020XXKB3 androidboot.info=0x4,0x0,1 androidboot.carrier=EUR gain_code=3 s3cfb.bootloaderfb=0x34a00000 mach-herring.lcd_type=0x00000000 oem_state=unlocked"
115
+CONFIG_CMDLINE_FORCE=y
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 # CONFIG_XIP_KERNEL is not set
117
 # CONFIG_KEXEC is not set
118
 
119
@@ -823,8 +823,6 @@ CONFIG_UEVENT_HELPER_PATH=""
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 CONFIG_STANDALONE=y
121
 CONFIG_PREVENT_FIRMWARE_BUILD=y
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 # CONFIG_FW_LOADER is not set
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-# CONFIG_FIRMWARE_IN_KERNEL is not set
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-CONFIG_EXTRA_FIRMWARE=""
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 # CONFIG_DEBUG_DRIVER is not set
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 # CONFIG_DEBUG_DEVRES is not set
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 # CONFIG_SYS_HYPERVISOR is not set
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@@ -835,7 +833,7 @@ CONFIG_MTD=y
129
 CONFIG_MTD_CONCAT=y
130
 CONFIG_MTD_PARTITIONS=y
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 # CONFIG_MTD_REDBOOT_PARTS is not set
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-# CONFIG_MTD_CMDLINE_PARTS is not set
133
+CONFIG_MTD_CMDLINE_PARTS=y
134
 # CONFIG_MTD_AFS_PARTS is not set
135
 # CONFIG_MTD_AR7_PARTS is not set
136
 
137
@@ -1191,6 +1189,7 @@ CONFIG_DEVKMEM=y
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 CONFIG_SERIAL_SAMSUNG=y
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 CONFIG_SERIAL_SAMSUNG_UARTS_4=y
140
 CONFIG_SERIAL_SAMSUNG_UARTS=4
141
+# CONFIG_SERIAL_SAMSUNG_DEBUG is not set
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 CONFIG_SERIAL_SAMSUNG_CONSOLE=y
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 CONFIG_SERIAL_S5PV210=y
144
 # CONFIG_SERIAL_MAX3100 is not set
145
@@ -2046,7 +2045,9 @@ CONFIG_HAVE_ARCH_KGDB=y
146
 CONFIG_DEBUG_USER=y
147
 CONFIG_DEBUG_ERRORS=y
148
 # CONFIG_DEBUG_STACK_USAGE is not set
149
-# CONFIG_DEBUG_LL is not set
150
+CONFIG_DEBUG_LL=y
151
+CONFIG_EARLY_PRINTK=y
152
+# CONFIG_DEBUG_ICEDCC is not set
153
 CONFIG_OC_ETM=y
154
 CONFIG_DEBUG_S3C_UART=2
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156
diff --git a/arch/arm/mach-s5pv210/dev-herring-phone.c b/arch/arm/mach-s5pv210/dev-herring-phone.c
157
index f8798b3..ecef636 100755
158
--- a/arch/arm/mach-s5pv210/dev-herring-phone.c
159
+++ b/arch/arm/mach-s5pv210/dev-herring-phone.c
160
@@ -48,8 +48,8 @@ static struct resource mdmctl_res[] = {
161
 	},
162
 	[2] = {
163
 		.name = "onedram",
164
-		.start = (S5PV210_PA_SDRAM + 0x05000000),
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-		.end = (S5PV210_PA_SDRAM + 0x05000000 + SZ_16M - 1),
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+		.start = (0x30000000  + 0x05000000),
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+		.end = (0x30000000  + 0x05000000 + SZ_16M - 1),
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 		.flags = IORESOURCE_MEM,
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 	},
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 };
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diff --git a/arch/arm/mach-s5pv210/mach-herring.c b/arch/arm/mach-s5pv210/mach-herring.c
172
index c3a0182..67fa1cf 100755
173
--- a/arch/arm/mach-s5pv210/mach-herring.c
174
+++ b/arch/arm/mach-s5pv210/mach-herring.c
175
@@ -5494,21 +5494,17 @@ static void __init herring_fixup(struct machine_desc *desc,
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 		struct tag *tags, char **cmdline,
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 		struct meminfo *mi)
178
 {
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-	mi->bank[0].start = 0x30000000;
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-	mi->bank[0].size = 80 * SZ_1M;
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+	mi->bank[0].start = 0x40000000;
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+	mi->bank[0].size = 256 * SZ_1M;
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 	mi->bank[0].node = 0;
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185
-	mi->bank[1].start = 0x40000000;
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-	mi->bank[1].size = 256 * SZ_1M;
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-	mi->bank[1].node = 1;
188
-
189
-	mi->bank[2].start = 0x50000000;
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+	mi->bank[1].start = 0x50000000;
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 	/* 1M for ram_console buffer */
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-	mi->bank[2].size = 127 * SZ_1M;
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-	mi->bank[2].node = 2;
194
-	mi->nr_banks = 3;
195
+	mi->bank[1].size = 127 * SZ_1M;
196
+	mi->bank[1].node = 1;
197
+	mi->nr_banks = 2;
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199
-	ram_console_start = mi->bank[2].start + mi->bank[2].size;
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+	ram_console_start = mi->bank[1].start + mi->bank[1].size;
201
 	ram_console_size = SZ_1M - SZ_4K;
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203
 	pm_debug_scratchpad = ram_console_start + ram_console_size;
204
</pre>
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<pre>
207
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
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index fff6d1b..c09d935 100755
209
--- a/BoardConfigCommon.mk
210
+++ b/BoardConfigCommon.mk
211
@@ -51,10 +51,10 @@ DEFAULT_FB_NUM := 2
212
 
213
 BOARD_NAND_PAGE_SIZE := 4096 -s 128
214
 
215
-BOARD_KERNEL_BASE := 0x30000000
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+BOARD_KERNEL_BASE := 0x40000000
217
 BOARD_KERNEL_PAGESIZE := 4096
218
-BOARD_KERNEL_CMDLINE := console=ttyFIQ0 no_console_suspend
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-
220
+BOARD_KERNEL_CMDLINE := console=ttyFIQ0 no_console_suspend earlyprintk=serial,ttySAC2,115200 bootmem_debug
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+BOARD_FORCE_RAMDISK_ADDRESS := 0x41000000
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 #TARGET_RECOVERY_UI_LIB := librecovery_ui_crespo
223
 TARGET_RELEASETOOLS_EXTENSIONS := device/samsung/crespo
224
</pre>