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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id co20sm6203964pjb.32.2021.04.01.16.23.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Apr 2021 16:23:54 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v10 6/6] lkdtm: Add REPORT_STACK for checking stack offsets Date: Thu, 1 Apr 2021 16:23:47 -0700 Message-Id: <20210401232347.2791257-7-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210401232347.2791257-1-keescook@chromium.org> References: <20210401232347.2791257-1-keescook@chromium.org> MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=04ba1fd2cf94c15b6c425d21eadf26c7b5b595c9; i=b69wRsxT78r/3tM1mGa7N6ME6+rlXyFg15giRWRwPAQ=; m=XEkb9gtEVwIXoR3CRFWDIQGhFt30zOfIashAyp1d4uo=; p=d33GDHyvnRxlVkBNxjBj+O38zle2N7FWLUDCSfaX1O0= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBmVgMACgkQiXL039xtwCaFWBAAnoV bf3FCj1tsOpxawVbSq+bVH2eLNWxW93P/OuD2SZViYnIltHwsMQb5O5JgjncW8xaOmaxRSKlAHAun c8QcJmj4OtK9gw6w9RGgvv/IFpIerKQ9rmBX1g3E9pYYL9w3c9VPWCCEy/n7JmUxYQRdueDWTFxbM DJcbI5C+2IcnzFrLA9H+wols1KqBnYq+b4dXGbk5komriRvkgReB+BDYk0Xk+CETCOSiHLluDFQBB o4m/PZXGsdWMD8Te1U+mf9I5VkhN/tQx3X4hchBhH1+Nmia+fhRki75vFi4V+nSg9uUwxBrnbvy0e wb+gePWPXj9YaEOUMwEy+OS6/ZvEFF4iXdsIokIGW7FylzIQnFltv1/iqj88+OPI+ptCESfD+jqyo h4VlZj/uVKKzJVktDMm8BrXCZTYeRD8ZvvxcTZRpdpSwPPH/p04bvjvs95CmBvn49r+7IpnVrUsH6 Q5EEB2mMj3/08pFtDtKkLRJi0b103YakkJghevfP1cQS6TlRL/XsKiM3v5UVjaH+OToPHUDfUCxSt ZzVucB9RlDb5QHXAW/55qYH2YKkEVAZt0B72UH+tH1XCxNucHUz84/Da5+eVTToByC7in/7nXdNU0 QHf1hWPssVLB1w4iS8kzT09u4F86a4AlFf/lxJmVXI1e4coBbEsRlccoJFqqRc7s= Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org For validating the stack offset behavior, report the offset from a given process's first seen stack address. Add script to calculate the results to the LKDTM kselftests. Signed-off-by: Kees Cook --- drivers/misc/lkdtm/bugs.c | 17 +++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + tools/testing/selftests/lkdtm/.gitignore | 1 + tools/testing/selftests/lkdtm/Makefile | 1 + .../testing/selftests/lkdtm/stack-entropy.sh | 36 +++++++++++++++++++ 6 files changed, 57 insertions(+) create mode 100755 tools/testing/selftests/lkdtm/stack-entropy.sh diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 110f5a8538e9..0e8254d0cf0b 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -134,6 +134,23 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void) __lkdtm_CORRUPT_STACK((void *)&data); } +static pid_t stack_pid; +static unsigned long stack_addr; + +void lkdtm_REPORT_STACK(void) +{ + volatile uintptr_t magic; + pid_t pid = task_pid_nr(current); + + if (pid != stack_pid) { + pr_info("Starting stack offset tracking for pid %d\n", pid); + stack_pid = pid; + stack_addr = (uintptr_t)&magic; + } + + pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic)); +} + void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) { static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index b2aff4d87c01..8024b6a5cc7f 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -110,6 +110,7 @@ static const struct crashtype crashtypes[] = { CRASHTYPE(EXHAUST_STACK), CRASHTYPE(CORRUPT_STACK), CRASHTYPE(CORRUPT_STACK_STRONG), + CRASHTYPE(REPORT_STACK), CRASHTYPE(CORRUPT_LIST_ADD), CRASHTYPE(CORRUPT_LIST_DEL), CRASHTYPE(STACK_GUARD_PAGE_LEADING), diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index 5ae48c64df24..99f90d3e5e9c 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -17,6 +17,7 @@ void lkdtm_LOOP(void); void lkdtm_EXHAUST_STACK(void); void lkdtm_CORRUPT_STACK(void); void lkdtm_CORRUPT_STACK_STRONG(void); +void lkdtm_REPORT_STACK(void); void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void); void lkdtm_SOFTLOCKUP(void); void lkdtm_HARDLOCKUP(void); 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 -- 2.25.1