On 6/29/25 8:02 PM, Huang Shijie wrote:
> As per admin guide documentation, "rodata=on" should be the default on
> platforms. Documentation/admin-guide/kernel-parameters.txt describes
> these options as
>
> rodata= [KNL,EARLY]
> on Mark read-only kernel memory as read-only (default).
> off Leave read-only kernel memory writable for debugging.
> full Mark read-only kernel memory and aliases as read-only
> [arm64]
>
> But on arm64 platform, "rodata=full" is the default instead. This patch
> implements the following changes.
>
> - Make "rodata=on" behaviour same as the original "rodata=full"
> - Make "rodata=noalias" (new) behaviour same as the original "rodata=on"
> - Drop the original "rodata=full"
> - Add comment for arch_parse_debug_rodata()
> - Update kernel-parameters.txt as required
>
> After this patch, the "rodata=on" will be the default on arm64 platform
> as well.
>
> Signed-off-by: Huang Shijie <shijie@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> .../admin-guide/kernel-parameters.txt | 2 +-
> arch/arm64/include/asm/setup.h | 28 +++++++++++++++++--
> 2 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index ee0735c6b8e2..e0cd6dac26d3 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6354,7 +6354,7 @@
> rodata= [KNL,EARLY]
> on Mark read-only kernel memory as read-only (default).
> off Leave read-only kernel memory writable for debugging.
> - full Mark read-only kernel memory and aliases as read-only
> + noalias Use more block mappings,may have better performance.
Add space after comma, please. ^
> [arm64]
>
> rockchip.usb_uart
> diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
> index ba269a7a3201..6b994d0881d1 100644
> --- a/arch/arm64/include/asm/setup.h
> +++ b/arch/arm64/include/asm/setup.h
> @@ -13,6 +13,30 @@
> extern phys_addr_t __fdt_pointer __initdata;
> extern u64 __cacheline_aligned boot_args[4];
>
> +/*
> + * rodata=on (default)
> + *
> + * This applies read-only attributes to VM areas and to the linear
> + * alias of the backing pages as well. This prevents code or read-
> + * only data from being modified (inadvertently or intentionally),
> + * via another mapping for the same memory page.
> + *
> + * But this might cause linear map region to be mapped down to base
> + * pages, which may adversely affect performance in some cases.
> + *
> + * rodata=off
> + *
> + * This provides more block mappings and contiguous hints for linear
> + * map region which would minimize TLB footprint. This also leaves
> + * read-only kernel memory writable for debugging.
> + *
> + * rodata=noalias
> + *
> + * This provides more block mappings and contiguous hints for linear
> + * map region which would minimize TLB footprint. This leaves the linear
> + * alias of read-only mappings in the vmalloc space writeable, making
> + * them susceptible to inadvertent modification by software.
> + */
> static inline bool arch_parse_debug_rodata(char *arg)
> {
> extern bool rodata_enabled;
> @@ -21,7 +45,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> if (!arg)
> return false;
>
> - if (!strcmp(arg, "full")) {
> + if (!strcmp(arg, "on")) {
> rodata_enabled = rodata_full = true;
> return true;
> }
> @@ -31,7 +55,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> return true;
> }
>
> - if (!strcmp(arg, "on")) {
> + if (!strcmp(arg, "noalias")) {
> rodata_enabled = true;
> rodata_full = false;
> return true;
--
~Randy
