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author | Sandrine Bailleux <sandrine.bailleux@arm.com> | 2016-07-08 14:37:40 +0100 |
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committer | Sandrine Bailleux <sandrine.bailleux@arm.com> | 2016-07-08 14:55:11 +0100 |
commit | 5d1c104f9aa7e1f52607679db96e5695cac266e7 (patch) | |
tree | 26daaf26d64ef7698da3920c0dd654963f2a92a8 /include/common | |
parent | 0146ae64c006956a281865f5688858d4846c781e (diff) |
Introduce SEPARATE_CODE_AND_RODATA build flag
At the moment, all BL images share a similar memory layout: they start
with their code section, followed by their read-only data section.
The two sections are contiguous in memory. Therefore, the end of the
code section and the beginning of the read-only data one might share
a memory page. This forces both to be mapped with the same memory
attributes. As the code needs to be executable, this means that the
read-only data stored on the same memory page as the code are
executable as well. This could potentially be exploited as part of
a security attack.
This patch introduces a new build flag called
SEPARATE_CODE_AND_RODATA, which isolates the code and read-only data
on separate memory pages. This in turn allows independent control of
the access permissions for the code and read-only data.
This has an impact on memory footprint, as padding bytes need to be
introduced between the code and read-only data to ensure the
segragation of the two. To limit the memory cost, the memory layout
of the read-only section has been changed in this case.
- When SEPARATE_CODE_AND_RODATA=0, the layout is unchanged, i.e.
the read-only section still looks like this (padding omitted):
| ... |
+-------------------+
| Exception vectors |
+-------------------+
| Read-only data |
+-------------------+
| Code |
+-------------------+ BLx_BASE
In this case, the linker script provides the limits of the whole
read-only section.
- When SEPARATE_CODE_AND_RODATA=1, the exception vectors and
read-only data are swapped, such that the code and exception
vectors are contiguous, followed by the read-only data. This
gives the following new layout (padding omitted):
| ... |
+-------------------+
| Read-only data |
+-------------------+
| Exception vectors |
+-------------------+
| Code |
+-------------------+ BLx_BASE
In this case, the linker script now exports 2 sets of addresses
instead: the limits of the code and the limits of the read-only
data. Refer to the Firmware Design guide for more details. This
provides platform code with a finer-grained view of the image
layout and allows it to map these 2 regions with the appropriate
access permissions.
Note that SEPARATE_CODE_AND_RODATA applies to all BL images.
Change-Id: I936cf80164f6b66b6ad52b8edacadc532c935a49
Diffstat (limited to 'include/common')
-rw-r--r-- | include/common/bl_common.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/include/common/bl_common.h b/include/common/bl_common.h index c43ad5ef..646a8172 100644 --- a/include/common/bl_common.h +++ b/include/common/bl_common.h @@ -143,8 +143,16 @@ * Declarations of linker defined symbols to help determine memory layout of * BL images */ +#if SEPARATE_CODE_AND_RODATA +extern unsigned long __TEXT_START__; +extern unsigned long __TEXT_END__; +extern unsigned long __RODATA_START__; +extern unsigned long __RODATA_END__; +#else extern unsigned long __RO_START__; extern unsigned long __RO_END__; +#endif + #if IMAGE_BL2 extern unsigned long __BL2_END__; #elif IMAGE_BL2U |