Re: [PATCH 5/6] driver core: Add __alloc_size hint to devm allocators

[Sami Tolvanen]

On Thu, Feb 2, 2023 at 11:53 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Thu, Feb 02, 2023 at 11:49:42AM -0800, Sami Tolvanen wrote:
> > A quick look at Clang's source code suggests that Intrinsic::ubsantrap
> > already accepts the handler ID (from the SanitizerHandler enum) as an
> > argument and the arm64 LLVM back-end appears to encode the value as an
> > immediate for the brk instruction. I didn't confirm that this actually
> > works, but perhaps we just need to teach the kernel about the possible
> > values?
>
> Oh excellent. Yeah, if that's all that's needed here that would be
> great. What are the values?

The arm64 brk immediate encoding seems to be "ubsantrap arg | 'U' << 8":

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64InstrInfo.td#L7571

The argument values come from the SanitizerHandler enum, which is
populated from this list:

https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenFunction.h#L113

Therefore, according to the tests, for ubsantrap(12) we'll get brk
#0x550c, for example:

https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/AArch64/ubsantrap.ll

Sami