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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>
31 lines
1 KiB
C
31 lines
1 KiB
C
/*
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* Copyright (c) 2017, 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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#ifndef CONSOLE_ASSERTIONS_H
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#define CONSOLE_ASSERTIONS_H
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#include <lib/cassert.h>
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/*
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* This file contains some separate assertions about console_t, moved here to
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* keep them out of the way. Should only be included from <console.h>.
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*/
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CASSERT(CONSOLE_T_NEXT == __builtin_offsetof(console_t, next),
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assert_console_t_next_offset_mismatch);
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CASSERT(CONSOLE_T_FLAGS == __builtin_offsetof(console_t, flags),
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assert_console_t_flags_offset_mismatch);
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CASSERT(CONSOLE_T_PUTC == __builtin_offsetof(console_t, putc),
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assert_console_t_putc_offset_mismatch);
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#if ENABLE_CONSOLE_GETC
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CASSERT(CONSOLE_T_GETC == __builtin_offsetof(console_t, getc),
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assert_console_t_getc_offset_mismatch);
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#endif
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CASSERT(CONSOLE_T_FLUSH == __builtin_offsetof(console_t, flush),
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assert_console_t_flush_offset_mismatch);
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CASSERT(CONSOLE_T_DRVDATA == sizeof(console_t),
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assert_console_t_drvdata_offset_mismatch);
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#endif /* CONSOLE_ASSERTIONS_H */
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