Messages in this thread |  | | Date | Mon, 19 Dec 2022 15:38:41 -0800 | From | Dan Li <> | Subject | Re: [RFC/RFT] CFI: Add support for gcc CFI in aarch64 |
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On 12/19, Peter Zijlstra wrote: > 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.
Oh ok, got it.
> 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. >
Yes, IIRC, long jumps also typically require at least three instructions in arm64.
Thanks, Dan.
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