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Fri, 25 Jul 2025 07:16:19 -0700 (PDT) Date: Fri, 25 Jul 2025 07:16:15 -0700 From: Deepak Gupta To: Heinrich Schuchardt Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, rick.p.edgecombe@intel.com, broonie@kernel.org, cleger@rivosinc.com, samitolvanen@google.com, apatel@ventanamicro.com, ajones@ventanamicro.com, conor.dooley@microchip.com, charlie@rivosinc.com, samuel.holland@sifive.com, bjorn@rivosinc.com, fweimer@redhat.com, jeffreyalaw@gmail.com, andrew@sifive.com, ved@rivosinc.com, Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nick Desaulniers , Bill Wendling , Monk Chiang , Kito Cheng , Justin Stitt Subject: Re: [PATCH 02/11] riscv: update asm call site in `call_on_irq_stack` to setup correct label Message-ID: References: <20250724-riscv_kcfi-v1-0-04b8fa44c98c@rivosinc.com> <20250724-riscv_kcfi-v1-2-04b8fa44c98c@rivosinc.com> <4ad699fc-a89d-4740-bdec-ecb9a2134c90@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <4ad699fc-a89d-4740-bdec-ecb9a2134c90@canonical.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D93F51A0017 X-Stat-Signature: wzjq4psdg7phbf6p5z7i1g3cr5qxkx89 X-HE-Tag: 1753452980-866705 X-HE-Meta: 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 XVIXvp9f 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jul 25, 2025 at 08:23:44AM +0200, Heinrich Schuchardt wrote: >On 25.07.25 01:36, Deepak Gupta wrote: >>Call sites written in asm performing indirect call, they need to setup >>label register (t2/x7) with correct label. >> >>Currently first kernel was compiled with `-save-temps` option and >>normalized function signature string is captured and then placed at the >>asm callsite. >> >>TODO: to write a macro wrapper with toolchain support. >> >>Signed-off-by: Deepak Gupta >>--- >> arch/riscv/kernel/entry.S | 1 + >> 1 file changed, 1 insertion(+) >> >>diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S >>index 2660faf52232..598e17e800ae 100644 >>--- a/arch/riscv/kernel/entry.S >>+++ b/arch/riscv/kernel/entry.S >>@@ -389,6 +389,7 @@ SYM_FUNC_START(call_on_irq_stack) >> load_per_cpu t0, irq_stack_ptr, t1 >> li t1, IRQ_STACK_SIZE >> add sp, t0, t1 >>+ lui t2, %lpad_hash("FvP7pt_regsE") > >In patch 1 you use lpad 0 due to missing tool support for signature hashing. > >Wouldn't it be preferable to have a first patch series introducing >landing pad support with lpad 0 and once tool support for signature >hashing has landed create a second patch series using tags? > >Such a first patch series would not have to be an RFC but might be >merged soon. It's mostly about security guarantees. Coarser grained cfi (only landing pad) has been proved many times not that effective. Kernel is a monolithic piece of code. If there is a good chance of adoption anywhere for labeled landing pads, its kernel. If it becomes a long pole, it's a possible direction to go back to unlabeled landing pad. > >Best regards > >Heinrich > >> jalr a1 >> /* Switch back to the thread shadow call stack */ >> >