linux-kernel - [PATCH -fixes v2] riscv: Check if the code to patch lies in the exit section

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Message-Id: <20231214091926.203439-1-alexghiti@rivosinc.com>
Date:   Thu, 14 Dec 2023 10:19:26 +0100
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Zong Li <zong.li@...ive.com>, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH -fixes v2] riscv: Check if the code to patch lies in the exit section

Otherwise we fall through to vmalloc_to_page() which panics since the
address does not lie in the vmalloc region.

Fixes: 043cb41a85de ("riscv: introduce interfaces to patch kernel code")
Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
---

Changes in v2:
- Fix XIP rv32 build failure

 arch/riscv/include/asm/sections.h   |  1 +
 arch/riscv/kernel/patch.c           | 11 ++++++++++-
 arch/riscv/kernel/vmlinux-xip.lds.S |  2 ++
 arch/riscv/kernel/vmlinux.lds.S     |  2 ++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
index 32336e8a17cb..a393d5035c54 100644
--- a/arch/riscv/include/asm/sections.h
+++ b/arch/riscv/include/asm/sections.h
@@ -13,6 +13,7 @@ extern char _start_kernel[];
 extern char __init_data_begin[], __init_data_end[];
 extern char __init_text_begin[], __init_text_end[];
 extern char __alt_start[], __alt_end[];
+extern char __exittext_begin[], __exittext_end[];
 
 static inline bool is_va_kernel_text(uintptr_t va)
 {
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 13ee7bf589a1..37e87fdcf6a0 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -14,6 +14,7 @@
 #include <asm/fixmap.h>
 #include <asm/ftrace.h>
 #include <asm/patch.h>
+#include <asm/sections.h>
 
 struct patch_insn {
 	void *addr;
@@ -25,6 +26,14 @@ struct patch_insn {
 int riscv_patch_in_stop_machine = false;
 
 #ifdef CONFIG_MMU
+
+static inline bool is_kernel_exittext(uintptr_t addr)
+{
+	return system_state < SYSTEM_RUNNING &&
+		addr >= (uintptr_t)__exittext_begin &&
+		addr < (uintptr_t)__exittext_end;
+}
+
 /*
  * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
  * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
@@ -35,7 +44,7 @@ static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
 	uintptr_t uintaddr = (uintptr_t) addr;
 	struct page *page;
 
-	if (core_kernel_text(uintaddr))
+	if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr))
 		page = phys_to_page(__pa_symbol(addr));
 	else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
 		page = vmalloc_to_page(addr);
diff --git a/arch/riscv/kernel/vmlinux-xip.lds.S b/arch/riscv/kernel/vmlinux-xip.lds.S
index 50767647fbc6..8c3daa1b0531 100644
--- a/arch/riscv/kernel/vmlinux-xip.lds.S
+++ b/arch/riscv/kernel/vmlinux-xip.lds.S
@@ -29,10 +29,12 @@ SECTIONS
 	HEAD_TEXT_SECTION
 	INIT_TEXT_SECTION(PAGE_SIZE)
 	/* we have to discard exit text and such at runtime, not link time */
+	__exittext_begin = .;
 	.exit.text :
 	{
 		EXIT_TEXT
 	}
+	__exittext_end = .;
 
 	.text : {
 		_text = .;
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 492dd4b8f3d6..002ca58dd998 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -69,10 +69,12 @@ SECTIONS
 		__soc_builtin_dtb_table_end = .;
 	}
 	/* we have to discard exit text and such at runtime, not link time */
+	__exittext_begin = .;
 	.exit.text :
 	{
 		EXIT_TEXT
 	}
+	__exittext_end = .;
 
 	__init_text_end = .;
 	. = ALIGN(SECTION_ALIGN);
-- 
2.39.2