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

[Charlie Jenkins]

On Thu, Dec 14, 2023 at 10:19:26AM +0100, Alexandre Ghiti wrote:
> 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@xxxxxxxxxxxx>
> ---
> 
> 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

Reviewed-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>

> 
> 
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