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authorLinus Torvalds <torvalds@linux-foundation.org>2021-04-26 10:02:09 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-04-26 10:02:09 -0700
commiteea2647e74cd7bd5d04861ce55fa502de165de14 (patch)
tree6d8fc43f3b8762651f825e74fc20f79d20f054a9 /tools
parent6f78c2a7b7219bc2e455250365f438621e5819d0 (diff)
parent70918779aec9bd01d16f4e6e800ffe423d196021 (diff)
downloadlinux-eea2647e74cd7bd5d04861ce55fa502de165de14.tar.bz2
Merge tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull entry code update from Thomas Gleixner: "Provide support for randomized stack offsets per syscall to make stack-based attacks harder which rely on the deterministic stack layout. The feature is based on the original idea of PaX's RANDSTACK feature, but uses a significantly different implementation. The offset does not affect the pt_regs location on the task stack as this was agreed on to be of dubious value. The offset is applied before the actual syscall is invoked. The offset is stored per cpu and the randomization happens at the end of the syscall which is less predictable than on syscall entry. The mechanism to apply the offset is via alloca(), i.e. abusing the dispised VLAs. This comes with the drawback that stack-clash-protection has to be disabled for the affected compilation units and there is also a negative interaction with stack-protector. Those downsides are traded with the advantage that this approach does not require any intrusive changes to the low level assembly entry code, does not affect the unwinder and the correct stack alignment is handled automatically by the compiler. The feature is guarded with a static branch which avoids the overhead when disabled. Currently this is supported for X86 and ARM64" * tag 'x86-entry-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: arm64: entry: Enable random_kstack_offset support lkdtm: Add REPORT_STACK for checking stack offsets x86/entry: Enable random_kstack_offset support stack: Optionally randomize kernel stack offset each syscall init_on_alloc: Optimize static branches jump_label: Provide CONFIG-driven build state defaults
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/lkdtm/.gitignore1
-rw-r--r--tools/testing/selftests/lkdtm/Makefile1
-rwxr-xr-xtools/testing/selftests/lkdtm/stack-entropy.sh36
3 files changed, 38 insertions, 0 deletions
diff --git a/tools/testing/selftests/lkdtm/.gitignore b/tools/testing/selftests/lkdtm/.gitignore
index f26212605b6b..d4b0be857deb 100644
--- a/tools/testing/selftests/lkdtm/.gitignore
+++ b/tools/testing/selftests/lkdtm/.gitignore
@@ -1,2 +1,3 @@
*.sh
!run.sh
+!stack-entropy.sh
diff --git a/tools/testing/selftests/lkdtm/Makefile b/tools/testing/selftests/lkdtm/Makefile
index 1bcc9ee990eb..c71109ceeb2d 100644
--- a/tools/testing/selftests/lkdtm/Makefile
+++ b/tools/testing/selftests/lkdtm/Makefile
@@ -5,6 +5,7 @@ include ../lib.mk
# NOTE: $(OUTPUT) won't get default value if used before lib.mk
TEST_FILES := tests.txt
+TEST_PROGS := stack-entropy.sh
TEST_GEN_PROGS = $(patsubst %,$(OUTPUT)/%.sh,$(shell awk '{print $$1}' tests.txt | sed -e 's/\#//'))
all: $(TEST_GEN_PROGS)
diff --git a/tools/testing/selftests/lkdtm/stack-entropy.sh b/tools/testing/selftests/lkdtm/stack-entropy.sh
new file mode 100755
index 000000000000..b1b8a5097cbb
--- /dev/null
+++ b/tools/testing/selftests/lkdtm/stack-entropy.sh
@@ -0,0 +1,36 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Measure kernel stack entropy by sampling via LKDTM's REPORT_STACK test.
+set -e
+samples="${1:-1000}"
+
+# Capture dmesg continuously since it may fill up depending on sample size.
+log=$(mktemp -t stack-entropy-XXXXXX)
+dmesg --follow >"$log" & pid=$!
+report=-1
+for i in $(seq 1 $samples); do
+ echo "REPORT_STACK" >/sys/kernel/debug/provoke-crash/DIRECT
+ if [ -t 1 ]; then
+ percent=$(( 100 * $i / $samples ))
+ if [ "$percent" -ne "$report" ]; then
+ /bin/echo -en "$percent%\r"
+ report="$percent"
+ fi
+ fi
+done
+kill "$pid"
+
+# Count unique offsets since last run.
+seen=$(tac "$log" | grep -m1 -B"$samples"0 'Starting stack offset' | \
+ grep 'Stack offset' | awk '{print $NF}' | sort | uniq -c | wc -l)
+bits=$(echo "obase=2; $seen" | bc | wc -L)
+echo "Bits of stack entropy: $bits"
+rm -f "$log"
+
+# We would expect any functional stack randomization to be at least 5 bits.
+if [ "$bits" -lt 5 ]; then
+ exit 1
+else
+ exit 0
+fi