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85bebe18da
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>
50 lines
1.1 KiB
ArmAsm
50 lines
1.1 KiB
ArmAsm
/*
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* Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <arch.h>
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#include <asm_macros.S>
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#include <console_macros.S>
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#include <assert_macros.S>
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#include "imx_uart.h"
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.globl console_imx_uart_register
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.globl console_imx_uart_putc
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.globl console_imx_uart_getc
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.globl console_imx_uart_flush
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func console_imx_uart_register
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push {r4, lr}
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mov r4, r3
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cmp r4, #0
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beq register_fail
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str r0, [r4, #CONSOLE_T_BASE]
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bl console_imx_uart_core_init
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cmp r0, #0
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bne register_fail
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mov r0, r4
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pop {r4, lr}
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finish_console_register imx_uart putc=1, getc=ENABLE_CONSOLE_GETC, flush=1
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register_fail:
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pop {r4, pc}
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endfunc console_imx_uart_register
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func console_imx_uart_putc
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ldr r1, [r1, #CONSOLE_T_BASE]
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b console_imx_uart_core_putc
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endfunc console_imx_uart_putc
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func console_imx_uart_getc
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ldr r0, [r0, #CONSOLE_T_BASE]
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b console_imx_uart_core_getc
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endfunc console_imx_uart_getc
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func console_imx_uart_flush
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ldr r0, [r0, #CONSOLE_T_BASE]
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b console_imx_uart_core_flush
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endfunc console_imx_uart_flush
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