On 2025-09-08 at 17:40:52 +0200, Peter Zijlstra wrote: >On Mon, Aug 18, 2025 at 08:26:11AM +0200, Maciej Wieczor-Retman wrote: >> On 2025-08-13 at 17:17:02 +0200, Peter Zijlstra wrote: >> >On Tue, Aug 12, 2025 at 03:23:49PM +0200, Maciej Wieczor-Retman wrote: >> >> Inline KASAN on x86 does tag mismatch reports by passing the faulty >> >> address and metadata through the INT3 instruction - scheme that's setup >> >> in the LLVM's compiler code (specifically HWAddressSanitizer.cpp). >> >> >> >> Add a kasan hook to the INT3 handling function. >> >> >> >> Disable KASAN in an INT3 core kernel selftest function since it can raise >> >> a false tag mismatch report and potentially panic the kernel. >> >> >> >> Make part of that hook - which decides whether to die or recover from a >> >> tag mismatch - arch independent to avoid duplicating a long comment on >> >> both x86 and arm64 architectures. >> >> >> >> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> >> > >> >Can we please split this into an arm64 and x86 patch. Also, why use int3 >> >here rather than a #UD trap, which we use for all other such cases? >> >> Sure, two patches seem okay. I'll first add all the new functions and modify the >> x86 code, then add the arm64 patch which will replace its die() + comment with >> kasan_inline_recover(). >> >> About INT3 I'm not sure, it's just how it's written in the LLVM code. I didn't >> see any justification why it's not #UD. My guess is SMD describes INT3 as an >> interrupt for debugger purposes while #UD is described as "for software >> testing". So from the documentation point INT3 seems to have a stronger case. >> >> Does INT3 interfere with something? Or is #UD better just because of >> consistency? > >INT3 from kernel space is already really tricky, since it is used for >self-modifying code. > >I suppose we *can* do this, but #UD is already set up to effectively >forward to WARN and friends, and has UBSAN integration. Its just really >weird to have KASAN do something else again. Ah, I see, the handle_bug(). Then perhaps it's better to move the kasan handler there and then patch LLVM to use #UD instead. Thanks! -- Kind regards Maciej Wieczór-Retman
