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Thu, 04 Sep 2025 21:49:50 -0700 (PDT) Message-ID: <68ba6bee.170a0220.3b821b.ca9d@mx.google.com> X-Google-Original-Message-ID: <87v7lxime4.fsf@ritesh.list@gmail.com> From: Ritesh Harjani (IBM) To: Christophe Leroy , Andrew Donnellan , Michael Ellerman , Nicholas Piggin , Madhavan Srinivasan Cc: Christophe Leroy , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Erhard Furtner Subject: Re: [PATCH] powerpc/32: Remove PAGE_KERNEL_TEXT to fix startup failure In-Reply-To: <4b5e6eb281d7b1ea77619bee17095f905a125168.1757003584.git.christophe.leroy@csgroup.eu> Date: Fri, 05 Sep 2025 09:25:15 +0530 References: <342b4120-911c-4723-82ec-d8c9b03a8aef@mailbox.org> <4b5e6eb281d7b1ea77619bee17095f905a125168.1757003584.git.christophe.leroy@csgroup.eu> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Christophe Leroy 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 > Closes: https://lore.kernel.org/all/342b4120-911c-4723-82ec-d8c9b03a8aef@mailbox.org/ > Signed-off-by: Christophe Leroy > --- > 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 > 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 > #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_X > > diff --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