Re: [PATCH] powerpc/32: Remove PAGE_KERNEL_TEXT to fix startup failure
From: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Date: 2025-09-05 04:49:52
Also in:
lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
Christophe Leroy [off-list ref] writes:
PAGE_KERNEL_TEXT is an old macro that is used to tell kernel whether kernel text has to be mapped read-only or read-write based on build time options. But nowadays, with functionnalities like jump_labels, static links, etc ... more only less all kernels need to be read-write at some point, and some combinations of configs failed to work due to innacurate setting of PAGE_KERNEL_TEXT. On the other hand, today we have CONFIG_STRICT_KERNEL_RWX which implements a more controlled access to kernel modifications. Instead of trying to keep PAGE_KERNEL_TEXT accurate with all possible options that may imply kernel text modification, always set kernel text read-write at startup and rely on CONFIG_STRICT_KERNEL_RWX to provide accurate protection. Reported-by: Erhard Furtner <redacted> Closes: https://lore.kernel.org/all/342b4120-911c-4723-82ec-d8c9b03a8aef@mailbox.org/ (local) Signed-off-by: Christophe Leroy <redacted> --- arch/powerpc/include/asm/pgtable.h | 12 ------------ arch/powerpc/mm/book3s32/mmu.c | 4 ++-- arch/powerpc/mm/pgtable_32.c | 2 +- 3 files changed, 3 insertions(+), 15 deletions(-)
AFAIU - mmu_mark_initmem_nx gets called during kernel_init() which is
way after static call initialization correct? i.e.
start_kernel
...
jump_label_init()
static_call_init()
...
...
rest_init() /* Do the rest non-__init'ed, we're now alive */
kernel_init()
free_initmem() -> mark_initmem_nx() -> __mark_initmem_nx -> mmu_mark_initmem_nx()
mark_readonly()
if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX) && rodata_enabled) {
jump_label_init_ro()
mark_rodata_ro() -> ....
...
...
Then I guess we mainly only need __mapin_ram_chunk() to be PAGE_KERNEL_X (RWX)
instead of PAGE_KERNEL_TEXT (ROX), isn't it?
Let me quickly validate it...
...Ok, so I was able to get just this diff to be working.
Thoughts?
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 15276068f657..0c9ef705803e 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c@@ -104,7 +104,7 @@ static void __init __mapin_ram_chunk(unsigned long offset, unsigned long top) p = memstart_addr + s; for (; s < top; s += PAGE_SIZE) { ktext = core_kernel_text(v); - map_kernel_page(v, p, ktext ? PAGE_KERNEL_TEXT : PAGE_KERNEL); + map_kernel_page(v, p, ktext ? PAGE_KERNEL_X : PAGE_KERNEL); v += PAGE_SIZE; p += PAGE_SIZE; } -ritesh
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 93d77ad5a92f..d8f944a5a037 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h@@ -20,18 +20,6 @@ struct mm_struct; #include <asm/nohash/pgtable.h> #endif /* !CONFIG_PPC_BOOK3S */ -/* - * Protection used for kernel text. We want the debuggers to be able to - * set breakpoints anywhere, so don't write protect the kernel text - * on platforms where such control is possible. - */ -#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_SWITCH) || \ - defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE) -#define PAGE_KERNEL_TEXT PAGE_KERNEL_X -#else -#define PAGE_KERNEL_TEXT PAGE_KERNEL_ROX -#endif - /* Make modules code happy. We don't set RO yet */ #define PAGE_KERNEL_EXEC PAGE_KERNEL_Xdiff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c index be9c4106e22f..c42ecdf94e48 100644 --- a/arch/powerpc/mm/book3s32/mmu.c +++ b/arch/powerpc/mm/book3s32/mmu.c@@ -204,7 +204,7 @@ int mmu_mark_initmem_nx(void) for (i = 0; i < nb - 1 && base < top;) { size = bat_block_size(base, top); - setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT); + setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X); base += size; } if (base < top) {@@ -215,7 +215,7 @@ int mmu_mark_initmem_nx(void) pr_warn("Some RW data is getting mapped X. " "Adjust CONFIG_DATA_SHIFT to avoid that.\n"); } - setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT); + setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X); base += size; } for (; i < nb; i++)diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c index 15276068f657..0c9ef705803e 100644 --- a/arch/powerpc/mm/pgtable_32.c +++ b/arch/powerpc/mm/pgtable_32.c@@ -104,7 +104,7 @@ static void __init __mapin_ram_chunk(unsigned long offset, unsigned long top) p = memstart_addr + s; for (; s < top; s += PAGE_SIZE) { ktext = core_kernel_text(v); - map_kernel_page(v, p, ktext ? PAGE_KERNEL_TEXT : PAGE_KERNEL); + map_kernel_page(v, p, ktext ? PAGE_KERNEL_X : PAGE_KERNEL); v += PAGE_SIZE; p += PAGE_SIZE; }-- 2.49.0