refactor(console): disable getc() by default
The ability to read a character from the console constitutes an attack
vector into TF-A, as it gives attackers a means to inject arbitrary
data into TF-A. It is dangerous to keep that feature enabled if not
strictly necessary, especially in production firmware builds.
Thus, we need a way to disable this feature. Moreover, when it is
disabled, all related code should be eliminated from the firmware
binaries, such that no remnant/dead getc() code remains in memory,
which could otherwise be used as a gadget as part of a bigger security
attack.
This patch disables getc() feature by default. For legitimate getc()
use cases [1], it can be explicitly enabled by building TF-A with
ENABLE_CONSOLE_GETC=1.
The following changes are introduced when getc() is disabled:
- The multi-console framework no longer provides the console_getc()
function.
- If the console driver selected by the platform attempts to register
a getc() callback into the multi-console framework then TF-A will
now fail to build.
If registered through the assembly function finish_console_register():
- On AArch64, you'll get:
Error: undefined symbol CONSOLE_T_GETC used as an immediate value.
- On AArch32, you'll get:
Error: internal_relocation (type: OFFSET_IMM) not fixed up
If registered through the C function console_register(), this requires
populating a struct console with a getc field, which will trigger:
error: 'console_t' {aka 'struct console'} has no member named 'getc'
- All console drivers which previously registered a getc() callback
have been modified to do so only when ENABLE_CONSOLE_GETC=1.
[1] Example of such use cases would be:
- Firmware recovery: retrieving a golden BL2 image over the console in
order to repair a broken firmware on a bricked board.
- Factory CLI tool: Drive some soak tests through the console.
Discussed on TF-A mailing list here:
https://lists.trustedfirmware.org/archives/list/tf-a@lists.trustedfirmware.org/thread/YS7F6RCNTWBTEOBLAXIRTXWIOYINVRW7/
Change-Id: Icb412304cd23dbdd7662df7cf8992267b7975cc5
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Acked-by: Baruch Siach <baruch@tkos.co.il>
diff --git a/plat/imx/common/aarch32/imx_uart_console.S b/plat/imx/common/aarch32/imx_uart_console.S
index 1a1229a..2a35b5e 100644
--- a/plat/imx/common/aarch32/imx_uart_console.S
+++ b/plat/imx/common/aarch32/imx_uart_console.S
@@ -28,7 +28,7 @@
mov r0, r4
pop {r4, lr}
- finish_console_register imx_uart putc=1, getc=1, flush=1
+ finish_console_register imx_uart putc=1, getc=ENABLE_CONSOLE_GETC, flush=1
register_fail:
pop {r4, pc}
diff --git a/plat/imx/common/imx_uart_console.S b/plat/imx/common/imx_uart_console.S
index 4d17288..560db15 100644
--- a/plat/imx/common/imx_uart_console.S
+++ b/plat/imx/common/imx_uart_console.S
@@ -33,7 +33,7 @@
mov x0, x6
mov x30, x7
- finish_console_register imx_uart putc=1, getc=1, flush=1
+ finish_console_register imx_uart putc=1, getc=ENABLE_CONSOLE_GETC, flush=1
register_fail:
ret x7
diff --git a/plat/imx/common/lpuart_console.S b/plat/imx/common/lpuart_console.S
index ff01e35..7acf773 100644
--- a/plat/imx/common/lpuart_console.S
+++ b/plat/imx/common/lpuart_console.S
@@ -27,7 +27,7 @@
mov x0, x6
mov x30, x7
- finish_console_register lpuart putc=1, getc=1, flush=1
+ finish_console_register lpuart putc=1, getc=ENABLE_CONSOLE_GETC, flush=1
register_fail:
ret x7
diff --git a/plat/nvidia/tegra/drivers/spe/shared_console.S b/plat/nvidia/tegra/drivers/spe/shared_console.S
index d1b18dd..5ad4eb8 100644
--- a/plat/nvidia/tegra/drivers/spe/shared_console.S
+++ b/plat/nvidia/tegra/drivers/spe/shared_console.S
@@ -71,7 +71,7 @@
cbz x3, register_fail
str x0, [x3, #CONSOLE_T_BASE]
mov x0, x3
- finish_console_register spe putc=1, getc=1, flush=1
+ finish_console_register spe putc=1, getc=ENABLE_CONSOLE_GETC, flush=1
register_fail:
mov w0, wzr
diff --git a/plat/socionext/uniphier/uniphier_console_setup.c b/plat/socionext/uniphier/uniphier_console_setup.c
index 9fda26e..9268f5d 100644
--- a/plat/socionext/uniphier/uniphier_console_setup.c
+++ b/plat/socionext/uniphier/uniphier_console_setup.c
@@ -30,7 +30,9 @@
CONSOLE_FLAG_CRASH |
CONSOLE_FLAG_TRANSLATE_CRLF,
.putc = uniphier_console_putc,
+#if ENABLE_CONSOLE_GETC
.getc = uniphier_console_getc,
+#endif
.flush = uniphier_console_flush,
};