Date: Thu, 2 Aug 2018 15:21:29 +0200 From: Ard Biesheuvel <ard.biesheuvel@...aro.org> To: kernel-hardening@...ts.openwall.com Cc: keescook@...omium.org, christoffer.dall@....com, will.deacon@....com, catalin.marinas@....com, mark.rutland@....com, labbott@...oraproject.org, linux-arm-kernel@...ts.infradead.org, Ard Biesheuvel <ard.biesheuvel@...aro.org> Subject: [RFC/PoC PATCH 0/3] arm64: basic ROP mitigation This is a proof of concept I cooked up, primarily to trigger a discussion about whether there is a point to doing anything like this, and if there is, what the pitfalls are. Also, while I am not aware of any similar implementations, the idea is so simple that I would be surprised if nobody else thought of the same thing way before I did. The idea is that we can significantly limit the kernel's attack surface for ROP based attacks by clearing the stack pointer's sign bit before returning from a function, and setting it again right after proceeding from the [expected] return address. This should make it much more difficult to return to arbitrary gadgets, given that they rely on being chained to the next via a return address popped off the stack, and this is difficult when the stack pointer is invalid. Of course, 4 additional instructions per function return is not exactly for free, but they are just movs and adds, and leaf functions are disregarded unless they allocate a stack frame (this comes for free because simple_return insns are disregarded by the plugin) Please shoot, preferably with better ideas ... Ard Biesheuvel (3): arm64: use wrapper macro for bl/blx instructions from asm code gcc: plugins: add ROP shield plugin for arm64 arm64: enable ROP protection by clearing SP bit #55 across function returns arch/Kconfig | 4 + arch/arm64/Kconfig | 10 ++ arch/arm64/include/asm/assembler.h | 21 +++- arch/arm64/kernel/entry-ftrace.S | 6 +- arch/arm64/kernel/entry.S | 104 +++++++++------- arch/arm64/kernel/head.S | 4 +- arch/arm64/kernel/probes/kprobes_trampoline.S | 2 +- arch/arm64/kernel/sleep.S | 6 +- drivers/firmware/efi/libstub/Makefile | 3 +- scripts/Makefile.gcc-plugins | 7 ++ scripts/gcc-plugins/arm64_rop_shield_plugin.c | 116 ++++++++++++++++++ 11 files changed, 228 insertions(+), 55 deletions(-) create mode 100644 scripts/gcc-plugins/arm64_rop_shield_plugin.c -- 2.18.0
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