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authorDave Martin <Dave.Martin@arm.com>2020-03-16 16:50:45 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2020-03-16 17:19:48 +0000
commit8ef8f360cf30be12382f89ff48a57fbbd9b31c14 (patch)
tree6060caf0bfe50a4c370c86625b7325f6199b746a /Documentation
parent00e19ceec80b03a43f626f891fcc53e57919f1b3 (diff)
downloadlwn-8ef8f360cf30be12382f89ff48a57fbbd9b31c14.tar.gz
lwn-8ef8f360cf30be12382f89ff48a57fbbd9b31c14.zip
arm64: Basic Branch Target Identification support
This patch adds the bare minimum required to expose the ARMv8.5 Branch Target Identification feature to userspace. By itself, this does _not_ automatically enable BTI for any initial executable pages mapped by execve(). This will come later, but for now it should be possible to enable BTI manually on those pages by using mprotect() from within the target process. Other arches already using the generic mman.h are already using 0x10 for arch-specific prot flags, so we use that for PROT_BTI here. For consistency, signal handler entry points in BTI guarded pages are required to be annotated as such, just like any other function. This blocks a relatively minor attack vector, but comforming userspace will have the annotations anyway, so we may as well enforce them. Signed-off-by: Mark Brown <broonie@kernel.org> Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/arm64/cpu-feature-registers.rst2
-rw-r--r--Documentation/arm64/elf_hwcaps.rst5
2 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
index 41937a8091aa..314fa5bc2655 100644
--- a/Documentation/arm64/cpu-feature-registers.rst
+++ b/Documentation/arm64/cpu-feature-registers.rst
@@ -176,6 +176,8 @@ infrastructure:
+------------------------------+---------+---------+
| SSBS | [7-4] | y |
+------------------------------+---------+---------+
+ | BT | [3-0] | y |
+ +------------------------------+---------+---------+
4) MIDR_EL1 - Main ID Register
diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst
index 7dfb97dfe416..84a9fd2d41b4 100644
--- a/Documentation/arm64/elf_hwcaps.rst
+++ b/Documentation/arm64/elf_hwcaps.rst
@@ -236,6 +236,11 @@ HWCAP2_RNG
Functionality implied by ID_AA64ISAR0_EL1.RNDR == 0b0001.
+HWCAP2_BTI
+
+ Functionality implied by ID_AA64PFR0_EL1.BT == 0b0001.
+
+
4. Unused AT_HWCAP bits
-----------------------