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In order to test various backward-edge control flow integrity methods,
add a test that manipulates the return address on the stack. Currently
only arm64 Pointer Authentication and Shadow Call Stack is supported.
$ echo CFI_BACKWARD | cat >/sys/kernel/debug/provoke-crash/DIRECT
Under SCS, successful test of the mitigation is reported as:
lkdtm: Performing direct entry CFI_BACKWARD
lkdtm: Attempting unchecked stack return address redirection ...
lkdtm: ok: redirected stack return address.
lkdtm: Attempting checked stack return address redirection ...
lkdtm: ok: control flow unchanged.
Under PAC, successful test of the mitigation is reported by the PAC
exception handler:
lkdtm: Performing direct entry CFI_BACKWARD
lkdtm: Attempting unchecked stack return address redirection ...
lkdtm: ok: redirected stack return address.
lkdtm: Attempting checked stack return address redirection ...
Unable to handle kernel paging request at virtual address bfffffc0088d0514
Mem abort info:
ESR = 0x86000004
EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
[bfffffc0088d0514] address between user and kernel address ranges
...
If the CONFIGs are missing (or the mitigation isn't working), failure
is reported as:
lkdtm: Performing direct entry CFI_BACKWARD
lkdtm: Attempting unchecked stack return address redirection ...
lkdtm: ok: redirected stack return address.
lkdtm: Attempting checked stack return address redirection ...
lkdtm: FAIL: stack return address was redirected!
lkdtm: This is probably expected, since this kernel was built *without* CONFIG_ARM64_PTR_AUTH_KERNEL=y nor CONFIG_SHADOW_CALL_STACK=y
Co-developed-by: Dan Li <ashimida@linux.alibaba.com>
Signed-off-by: Dan Li <ashimida@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20220416001103.1524653-1-keescook@chromium.org
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