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Miller" , "David Ahern" , "Thomas Gleixner" , "Ingo Molnar" , "Borislav Petkov" , "Dave Hansen" , "X86 ML" , "H. Peter Anvin" , "Shuah Khan" , "Maxime Coquelin" , "Alexandre Torgue" , "Andrey Ryabinin" , "Alexander Potapenko" , "Andrey Konovalov" , "Dmitry Vyukov" , "Vincenzo Frascino" , "Andrew Morton" , , "Bastien Curutchet" , "Thomas Petazzoni" , "Xu Kuohai" , "bpf" , "LKML" , "Network Development" , "open list:KERNEL SELFTEST FRAMEWORK" , , "linux-arm-kernel" , "kasan-dev" , "linux-mm" From: =?utf-8?q?Alexis_Lothor=C3=A9?= To: "Alexei Starovoitov" , "Ihor Solodrai" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260413-kasan-v1-0-1a5831230821@bootlin.com> <71fb19ff-6dde-43f4-a0e9-5c8cf2ba4ed4@linux.dev> In-Reply-To: X-Last-TLS-Session-Version: TLSv1.3 X-Rspam-User: X-Rspamd-Queue-Id: 029D41C000E X-Rspamd-Server: rspam06 X-Stat-Signature: d7y9zqko484weaqfdftm6wqk1kxaygd7 X-HE-Tag: 1777280077-528396 X-HE-Meta: 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 ukJ05VjG /F48AebGtK/6ODEuQm+nn9J1JfSVm2vqo5vFyQCLpcbUYbtBv9kNyc4/GdOJAIwysixif05WKbg7and8DXF0IKrOgGRDuke0p76nro/0Q4NwJdQdGaeTJvXTuEhDTGNxf7OC+wR+B4uZbHu/bPDxaLLWDzkxRw1cB+Y/Xm4oyWwq20eq+hLJ+Qx39dCjW2BVF/tK94bx26jBgMBJZQzalsVesSEzV5ohr7cX594TsOuunkm2Q4Ht8qoyZCfpKHSlyRj8O9/lLZWvchjmbhwOKLALp5C9oCRjy8F720ukpxamG3XoPYhaaDVB20Z+4FRLy9xGGTAsqVDwZTFnqFOo5O5biLD9dAHM7vo9K5+8Uy0oO3NDPEcDjS0cmsQf4PO3PTw2hFMX9QbeOPVkwl/MgXoUK325Ok/AC8zvuhTZjfUGdnHMOpxSezyfkDQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat Apr 25, 2026 at 1:28 AM CEST, Alexei Starovoitov wrote: > On Fri, Apr 24, 2026 at 4:10=E2=80=AFPM Ihor Solodrai wrote: >> >> I wonder if it's feasible to implement KASAN support on the verifier >> side in post-verification fixups. AI slop for illustration: >> >> ;; Original (1 BPF insn): >> dst =3D *(u64 *)(src + off) ; BPF_LDX | BPF_MEM | BPF_DW >> >> ;; Rewrite (~7 BPF insns): >> r_tmp1 =3D src ; BPF_MOV64_REG >> r_tmp1 +=3D off ; BPF_ALU64 | BPF_ADD | K (fu= ll address) >> r_tmp2 =3D r_tmp1 ; copy >> r_tmp2 >>=3D 3 ; KASAN_SHADOW_SCALE_SHIFT >> r_tmp2 +=3D KASAN_SHADOW_OFFSET ; shadow address >> r_tmp3 =3D *(u8 *)(r_tmp2 + 0) ; BPF_LDX | BPF_B (load shado= w byte) >> if r_tmp3 !=3D 0 goto +2 ; BPF_JNE | PC+2 >> dst =3D *(u64 *)(src + off) ; original access (fast path) >> goto +1 ; skip slowpath >> call __asan_report_load8 ; BPF kfunc >> dst =3D *(u64 *)(src + off) ; retry the access after report= (non-fatal) >> >> A sort of inline kasan directly in BPF. >> >> There are plenty of issues with it: instruction limit, exposing asan >> API as kfuncs, etc. On the flip side we get cross-arch support out of >> the box with no or mininal JIT changes. >> >> Honestly I'm not excited about this approach, but curious if anyone >> thought about this, or maybe it was already discussed? > > We discussed this. > It won't work because we don't have that many temp registers for once > and second it has to preserve all (both callee and caller saved regs). > This is arch specific. This "fast path" was indeed part of my initial proposal. For the record: https://lore.kernel.org/bpf/DG7UG112AVBC.JKYISDTAM30T@bootlin.com/ in the "Basic instrumentation" block. --=20 Alexis Lothor=C3=A9, Bootlin Embedded Linux and Kernel engineering https://bootlin.com