Messages in this thread Patch in this message | | | Date | Sun, 29 Jan 2006 21:56:53 +0100 | From | Eric Dumazet <> | Subject | [PATCH, V2] i386: instead of poisoning .init zone, change protection bits to force a fault |
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Chasing some invalid accesses to .init zone, I found that free_init_pages() was properly freeing the pages but virtual was still usable.
A poisoning (memset(page, 0xcc, PAGE_SIZE)) was done but this is not reliable.
A new config option DEBUG_INITDATA is introduced to mark this initdata as not present at all so that buggy code can trigger a fault.
This option is not meant for production machines because it may split one or two huge page (2MB or 4MB) into small pages and thus slow down kernel a bit.
(After that we could map non possible cpu percpu data to the initial percpudata that is included in .init and discarded in free_initmem())
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> --- a/arch/i386/Kconfig.debug 2006-01-29 22:30:10.000000000 +0100 +++ b/arch/i386/Kconfig.debug 2006-01-29 22:35:54.000000000 +0100 @@ -61,6 +61,18 @@ portion of the kernel code won't be covered by a 2MB TLB anymore. If in doubt, say "N". +config DEBUG_INITDATA + bool "Read/Write protect kernel init data structures" + depends on DEBUG_KERNEL + help + The init data is normally freed when kernel has booted. + Some code may still try to read or write to data in this area. + If you say Y here, the kernel will mark this zone as not readable + or writeable at all. Buggy code will then fault. + This option may have a slight performance impact because a + portion of the kernel code won't be covered by a 2MB TLB anymore. + If in doubt, say "N". + config 4KSTACKS bool "Use 4Kb + 4Kb for kernel stacks instead of 8Kb" if DEBUG_KERNEL default y --- a/arch/i386/mm/init.c 2006-01-25 10:17:24.000000000 +0100 +++ b/arch/i386/mm/init.c 2006-01-29 22:38:53.000000000 +0100 @@ -750,11 +750,18 @@ for (addr = begin; addr < end; addr += PAGE_SIZE) { ClearPageReserved(virt_to_page(addr)); set_page_count(virt_to_page(addr), 1); +#ifdef CONFIG_DEBUG_INITDATA + change_page_attr(virt_to_page(addr), 1, __pgprot(0)); +#else memset((void *)addr, 0xcc, PAGE_SIZE); +#endif free_page(addr); totalram_pages++; } printk(KERN_INFO "Freeing %s: %ldk freed\n", what, (end - begin) >> 10); +#ifdef CONFIG_DEBUG_INITDATA + global_flush_tlb(); +#endif } void free_initmem(void)
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