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Mon, 26 Oct 2026 13:13:56 -0700 (PDT) Received: from valdaarhun.localdomain ([2401:4900:1c44:61b8:f26f:bd5b:b550:7a07]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-198a020df20sm31730486c88.6.2026.10.26.13.13.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2026 13:13:56 -0700 (PDT) From: Sahil Siddiq To: jonas@southpole.se, stefan.kristiansson@saunalahti.fi, shorne@gmail.com, naveen@kernel.org, davem@davemloft.net, mhiramat@kernel.org Cc: pjw@kernel.org, wangruikang@iscas.ac.cn, namcao@linutronix.de, kees@kernel.org, linux-openrisc@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Sahil Siddiq Subject: [PATCH v3 4/4] openrisc: Add Kretprobes Date: Tue, 27 Oct 2026 01:42:40 +0530 Message-ID: <20261026201240.107462-5-sahilcdq0@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930202744.50489-1-sahilcdq0@gmail.com> References: <20260930202744.50489-1-sahilcdq0@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add Kretprobes support for OpenRISC. Kretprobes allow a probe to be fired when a function returns. They are built on top of the generic rethook framework and also require the KProbe mechanism introduced in the previous commit. This work is primarily based on similar work done for RISC-V. Kretprobes work by inserting a KProbe at a function's entry point. When the function begins to execute, the KProbe is fired and its pre-handler replaces the function's return address with that of the rethook trampoline. The trampoline in turn calls the kretprobe handler. Control is returned to the original caller following this. Signed-off-by: Sahil Siddiq --- Changes v2 -> v3: - arch/openrisc/kernel/rethook_trampoline.S: (save_all_base_regs): Save SR and SP registers (restore_all_base_regs): Restore SR register Changes v1 -> v2: New commit arch/openrisc/Kconfig | 2 + arch/openrisc/kernel/Makefile | 1 + arch/openrisc/kernel/rethook.c | 32 +++++++ arch/openrisc/kernel/rethook.h | 8 ++ arch/openrisc/kernel/rethook_trampoline.S | 111 ++++++++++++++++++++++ 5 files changed, 154 insertions(+) create mode 100644 arch/openrisc/kernel/rethook.c create mode 100644 arch/openrisc/kernel/rethook.h create mode 100644 arch/openrisc/kernel/rethook_trampoline.S diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig index d240533b424b..82365eb8f574 100644 --- a/arch/openrisc/Kconfig +++ b/arch/openrisc/Kconfig @@ -28,6 +28,8 @@ config OPENRISC select HAVE_ARCH_JUMP_LABEL_RELATIVE select HAVE_PCI select HAVE_KPROBES + select HAVE_KRETPROBES + select HAVE_RETHOOK select HAVE_UID16 select HAVE_PAGE_SIZE_8KB select HAVE_REGS_AND_STACK_ACCESS_API diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile index 0c1cade09e0c..e36537cea319 100644 --- a/arch/openrisc/kernel/Makefile +++ b/arch/openrisc/kernel/Makefile @@ -15,6 +15,7 @@ obj-$(CONFIG_STACKTRACE) += stacktrace.o obj-$(CONFIG_MODULES) += module.o obj-$(CONFIG_OF) += prom.o obj-$(CONFIG_KPROBES) += kprobes.o +obj-$(CONFIG_RETHOOK) += rethook.o rethook_trampoline.o obj-$(CONFIG_OR_KPROBES_KUNIT) += tests/ obj-y += patching.o diff --git a/arch/openrisc/kernel/rethook.c b/arch/openrisc/kernel/rethook.c new file mode 100644 index 000000000000..50ef6715d044 --- /dev/null +++ b/arch/openrisc/kernel/rethook.c @@ -0,0 +1,32 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Generic return hook for OpenRISC. Depends on KProbes. + * + * Linux architectural port borrowing liberally from similar works of + * others. All original copyrights apply as per the original source + * declaration. + * + * OpenRISC implementation: + * Copyright (C) 2026 Sahil Siddiq + */ + +#include +#include +#include "rethook.h" + +unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs) +{ + return rethook_trampoline_handler(regs, regs->gpr2); +} +NOKPROBE_SYMBOL(arch_rethook_trampoline_callback) + +void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount) +{ + /* Store original return address and frame pointer */ + rhn->ret_addr = regs->gpr9; + rhn->frame = regs->gpr2; + + /* Set return address to trampoline */ + regs->gpr9 = (unsigned long)arch_rethook_trampoline; +} +NOKPROBE_SYMBOL(arch_rethook_prepare) diff --git a/arch/openrisc/kernel/rethook.h b/arch/openrisc/kernel/rethook.h new file mode 100644 index 000000000000..332306a5c380 --- /dev/null +++ b/arch/openrisc/kernel/rethook.h @@ -0,0 +1,8 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +#ifndef __OPENRISC_RETHOOK_H +#define __OPENRISC_RETHOOK_H + +unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs); +void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount); + +#endif diff --git a/arch/openrisc/kernel/rethook_trampoline.S b/arch/openrisc/kernel/rethook_trampoline.S new file mode 100644 index 000000000000..5e8fd5a65222 --- /dev/null +++ b/arch/openrisc/kernel/rethook_trampoline.S @@ -0,0 +1,111 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Author: Sahil Siddiq + */ + +#include + +#include +#include +#include + + .text + + .macro save_all_base_regs + l.sw PT_GPR2(r1),r2 + l.sw PT_GPR3(r1),r3 + l.sw PT_GPR4(r1),r4 + l.sw PT_GPR5(r1),r5 + l.sw PT_GPR6(r1),r6 + l.sw PT_GPR7(r1),r7 + l.sw PT_GPR8(r1),r8 + l.sw PT_GPR9(r1),r9 + l.sw PT_GPR10(r1),r10 + l.sw PT_GPR11(r1),r11 + l.sw PT_GPR12(r1),r12 + l.sw PT_GPR13(r1),r13 + l.sw PT_GPR14(r1),r14 + l.sw PT_GPR15(r1),r15 + l.sw PT_GPR16(r1),r16 + l.sw PT_GPR17(r1),r17 + l.sw PT_GPR18(r1),r18 + l.sw PT_GPR19(r1),r19 + l.sw PT_GPR20(r1),r20 + l.sw PT_GPR21(r1),r21 + l.sw PT_GPR22(r1),r22 + l.sw PT_GPR23(r1),r23 + l.sw PT_GPR24(r1),r24 + l.sw PT_GPR25(r1),r25 + l.sw PT_GPR26(r1),r26 + l.sw PT_GPR27(r1),r27 + l.sw PT_GPR28(r1),r28 + l.sw PT_GPR29(r1),r29 + l.sw PT_GPR30(r1),r30 + l.sw PT_GPR31(r1),r31 + /* Save SR in pt_regs */ + l.mfspr r13,r0,SPR_SR + l.sw PT_SR(r1),r13 + /* Save SP in pt_regs as it was prior to setting up this frame */ + l.addi r13,r1,PT_SIZE + l.sw PT_SP(r1),r13 + .endm + + .macro restore_all_base_regs + /* Restore SR from pt_regs */ + l.lwz r13,PT_SR(r1) + l.mtspr r0,r13,SPR_SR + /* + * r1 doesn't need to be explicitly restored from pt_regs. When + * arch_rethook_trampoline_callback finishes, it restores SP to + * what it was before its frame was set up. + */ + l.lwz r2,PT_GPR2(r1) + l.lwz r3,PT_GPR3(r1) + l.lwz r4,PT_GPR4(r1) + l.lwz r5,PT_GPR5(r1) + l.lwz r6,PT_GPR6(r1) + l.lwz r7,PT_GPR7(r1) + l.lwz r8,PT_GPR8(r1) + /* Return address in r9 is stale, so don't restore it */ + l.lwz r10,PT_GPR10(r1) + l.lwz r11,PT_GPR11(r1) + l.lwz r12,PT_GPR12(r1) + l.lwz r13,PT_GPR13(r1) + l.lwz r14,PT_GPR14(r1) + l.lwz r15,PT_GPR15(r1) + l.lwz r16,PT_GPR16(r1) + l.lwz r17,PT_GPR17(r1) + l.lwz r18,PT_GPR18(r1) + l.lwz r19,PT_GPR19(r1) + l.lwz r20,PT_GPR20(r1) + l.lwz r21,PT_GPR21(r1) + l.lwz r22,PT_GPR22(r1) + l.lwz r23,PT_GPR23(r1) + l.lwz r24,PT_GPR24(r1) + l.lwz r25,PT_GPR25(r1) + l.lwz r26,PT_GPR26(r1) + l.lwz r27,PT_GPR27(r1) + l.lwz r28,PT_GPR28(r1) + l.lwz r29,PT_GPR29(r1) + l.lwz r30,PT_GPR30(r1) + l.lwz r31,PT_GPR31(r1) + .endm + +SYM_CODE_START(arch_rethook_trampoline) + /* Allocate enough space on stack for pt_regs */ + l.addi r1,r1,-PT_SIZE + save_all_base_regs + + l.addi r3,r1,0 /* pt_regs */ + l.jal arch_rethook_trampoline_callback + l.nop + + /* use the result as the return-address */ + l.addi r9,r11,0 + + restore_all_base_regs + l.addi r1,r1,PT_SIZE + + l.jr r9 + l.nop +SYM_CODE_END(arch_rethook_trampoline) -- 2.55.0