Re: [PATCH v5 2/2] riscv: patch: skip fixmap mapping when kernel text is already writable

On Fri, Aug 14, 2026 at 9:29 AM Xiaofeng Yuan <[email protected]> wrote:
>
> patch_map() always creates a temporary writable mapping via fixmap for
> kernel text addresses, even when CONFIG_STRICT_KERNEL_RWX is disabled
> and the kernel text is already mapped with _PAGE_WRITE.
>
> This is unnecessary overhead at best, and on minimal configurations
> it can cause page faults.
>
> Skip the fixmap path for kernel text when CONFIG_STRICT_KERNEL_RWX
> is not enabled, since the text pages are already writable in that case.
> The module text path is already gated on CONFIG_STRICT_MODULE_RWX and
> is kept unchanged.
>
> Reported-by: Klara Modin <[email protected]>
> Closes: https://lore.kernel.org/all/[email protected]/
> Reported-by: Lad Prabhakar <[email protected]>
> Closes: https://lore.kernel.org/all/CA+V-a8tQK8rih9SGGTyqrEBGpNkx4H0eX2YccCRrgkVAPr+EBg@mail.gmail.com/
> ---
> v5: fix the fixmap gating for kernel text. The v4 early return on
>     CONFIG_STRICT_MODULE_RWX wrongly skipped the fixmap for kernel text
>     too, which panics on configs with CONFIG_MODULES=n where
>     CONFIG_STRICT_MODULE_RWX is unavailable but CONFIG_STRICT_KERNEL_RWX
>     is still enabled and kernel text is read-only.
> v3: early return when !CONFIG_STRICT_MODULE_RWX (per Nam Cao's suggestion)
> v2: add commit description
>
> Signed-off-by: Xiaofeng Yuan <[email protected]>
> ---
>  arch/riscv/kernel/patch.c | 2 ++
>  1 file changed, 2 insertions(+)
>
Tested-by: Lad Prabhakar <[email protected]>

Cheers,
Prabhakar

> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 16b243376f..2239c28981 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -45,6 +45,8 @@ static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
>         phys_addr_t phys;
>
>         if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr)) {
> +               if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> +                       return addr;
>                 phys = __pa_symbol(addr);
>         } else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {
>                 struct page *page = vmalloc_to_page(addr);
> --
> 2.43.0
>

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