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authorAmit Daniel Kachhap <amit.kachhap@arm.com>2020-03-13 12:05:04 +0300
committerCatalin Marinas <catalin.marinas@arm.com>2020-03-18 12:50:21 +0300
commit6cb6982f42cbfaf5e50af1069451a8828231ffb9 (patch)
tree996008b08cb8dbb4aed73e0e3dbc3e71d817bb48 /drivers/misc/lkdtm
parent74afda4016a7437e6e425c3370e4b93b47be8ddf (diff)
downloadlinux-6cb6982f42cbfaf5e50af1069451a8828231ffb9.tar.xz
lkdtm: arm64: test kernel pointer authentication
This test is specific for arm64. When in-kernel Pointer Authentication config is enabled, the return address stored in the stack is signed. This feature helps in ROP kind of attack. If any parameters used to generate the pac (<key, sp, lr>) is modified then this will fail in the authentication stage and will lead to abort. This test changes the input parameter APIA kernel keys to cause abort. The pac computed from the new key can be same as last due to hash collision so this is retried for few times as there is no reliable way to compare the pacs. Even though this test may fail even after retries but this may cause authentication failure at a later stage in earlier function returns. This test can be invoked as, echo CORRUPT_PAC > /sys/kernel/debug/provoke-crash/DIRECT or as below if inserted as a module, insmod lkdtm.ko cpoint_name=DIRECT cpoint_type=CORRUPT_PAC cpoint_count=1 [ 13.118166] lkdtm: Performing direct entry CORRUPT_PAC [ 13.118298] lkdtm: Clearing PAC from the return address [ 13.118466] Unable to handle kernel paging request at virtual address bfff8000108648ec [ 13.118626] Mem abort info: [ 13.118666] ESR = 0x86000004 [ 13.118866] EC = 0x21: IABT (current EL), IL = 32 bits [ 13.118966] SET = 0, FnV = 0 [ 13.119117] EA = 0, S1PTW = 0 Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'drivers/misc/lkdtm')
-rw-r--r--drivers/misc/lkdtm/bugs.c36
-rw-r--r--drivers/misc/lkdtm/core.c1
-rw-r--r--drivers/misc/lkdtm/lkdtm.h1
3 files changed, 38 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index de87693cf557..cc92bc3ed820 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -378,3 +378,39 @@ void lkdtm_DOUBLE_FAULT(void)
pr_err("XFAIL: this test is ia32-only\n");
#endif
}
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+static noinline void change_pac_parameters(void)
+{
+ /* Reset the keys of current task */
+ ptrauth_thread_init_kernel(current);
+ ptrauth_thread_switch_kernel(current);
+}
+
+#define CORRUPT_PAC_ITERATE 10
+noinline void lkdtm_CORRUPT_PAC(void)
+{
+ int i;
+
+ if (!system_supports_address_auth()) {
+ pr_err("FAIL: arm64 pointer authentication feature not present\n");
+ return;
+ }
+
+ pr_info("Change the PAC parameters to force function return failure\n");
+ /*
+ * Pac is a hash value computed from input keys, return address and
+ * stack pointer. As pac has fewer bits so there is a chance of
+ * collision, so iterate few times to reduce the collision probability.
+ */
+ for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
+ change_pac_parameters();
+
+ pr_err("FAIL: %s test failed. Kernel may be unstable from here\n", __func__);
+}
+#else /* !CONFIG_ARM64_PTR_AUTH */
+noinline void lkdtm_CORRUPT_PAC(void)
+{
+ pr_err("FAIL: arm64 pointer authentication config disabled\n");
+}
+#endif
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index ee0d6e721441..5ce4ac8c06fc 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -116,6 +116,7 @@ static const struct crashtype crashtypes[] = {
CRASHTYPE(STACK_GUARD_PAGE_LEADING),
CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
CRASHTYPE(UNSET_SMEP),
+ CRASHTYPE(CORRUPT_PAC),
CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
CRASHTYPE(OVERWRITE_ALLOCATION),
CRASHTYPE(WRITE_AFTER_FREE),
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index c56d23e37643..8d13d0176624 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -31,6 +31,7 @@ void lkdtm_UNSET_SMEP(void);
#ifdef CONFIG_X86_32
void lkdtm_DOUBLE_FAULT(void);
#endif
+void lkdtm_CORRUPT_PAC(void);
/* lkdtm_heap.c */
void __init lkdtm_heap_init(void);