[PATCH] arm64: mm: Fix "rodata=on" when CONFIG_RODATA_FULL_DEFAULT_ENABLED=y

Will Deacon
2023-11-17T13:15:11Z

When CONFIG_RODATA_FULL_DEFAULT_ENABLED=y, passing "rodata=on" on the
kernel command-line (rather than "rodata=full") should turn off the
"full" behaviour, leaving writable linear aliases of read-only kernel
memory. Unfortunately, the option has no effect in this situation and
the only way to disable the "rodata=full" behaviour is to disable rodata
protection entirely by passing "rodata=off".

Fix this by parsing the "on" and "off" options in the arch code,
additionally enforcing that 'rodata_full' cannot be set without also
setting 'rodata_enabled', allowing us to simplify a couple of checks
in the process.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/setup.h | 17 +++++++++++++++--
arch/arm64/mm/pageattr.c | 7 +++----
2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
index f4af547ef54c..2e4d7da74fb8 100644
--- a/arch/arm64/include/asm/setup.h
+++ b/arch/arm64/include/asm/setup.h
@@ -21,9 +21,22 @@ static inline bool arch_parse_debug_rodata(char *arg)
extern bool rodata_enabled;
extern bool rodata_full;

- if (arg && !strcmp(arg, "full")) {
+ if (!arg)
+ return false;
+
+ if (!strcmp(arg, "full")) {
+ rodata_enabled = rodata_full = true;
+ return true;
+ }
+
+ if (!strcmp(arg, "off")) {
+ rodata_enabled = rodata_full = false;
+ return true;
+ }
+
+ if (!strcmp(arg, "on")) {
rodata_enabled = true;
- rodata_full = true;
+ rodata_full = false;
return true;
}

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 8e2017ba5f1b..924843f1f661 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -29,8 +29,8 @@ bool can_set_direct_map(void)
*
* KFENCE pool requires page-granular mapping if initialized late.
*/
- return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
- arm64_kfence_can_set_direct_map();
+ return rodata_full || debug_pagealloc_enabled() ||
+ arm64_kfence_can_set_direct_map();
}

static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
@@ -105,8 +105,7 @@ static int change_memory_common(unsigned long addr, int numpages,
* If we are manipulating read-only permissions, apply the same
* change to the linear mapping of the pages that back this VM area.
*/
- if (rodata_enabled &&
- rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
+ if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
pgprot_val(clear_mask) == PTE_RDONLY)) {
for (i = 0; i < area->nr_pages; i++) {
__change_memory_common((u64)page_address(area->pages[i]),
--
2.43.0.rc0.421.g78406f8d94-goog