Messages in this thread |  | | Date | Mon, 19 Dec 2022 16:04:55 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC/RFT] CFI: Add support for gcc CFI in aarch64 |
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On Mon, Dec 19, 2022 at 05:32:04AM -0800, Dan Li wrote: > Hi Peter, > > On 12/19, Peter Zijlstra wrote: > > On Sun, Dec 18, 2022 at 10:17:58PM -0800, Dan Li wrote: > > > > > 1. When a typeid mismatch is detected, the cfi_check_failed function > > > will be called instead of the brk instruction. This function needs > > > to be implemented by the compiler user. > > > If there are user mode programs or other systems that want to use > > > this feature, it may be more convenient to use a callback (so this > > > compilation option is set to -fsanitize=cfi instead of kcfi). > > > > This is not going to be acceptible for x86_64. > > I'm not familiar enough with the x86_64 platform, could you please > tell me why this is not acceptable? Is there a similar situation > on the arm64 platform?
Mostly because the call would be a 5 byte instruction while the trap (UD2) is only 2 bytes.
I suspect Argh64 has a similar problem if the to be called function is outside the immediate range (26 bits or thereabout), in which case you end up with a multi-instruction sequence to construct the call target or so. A trap is always a single instruction.
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