Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756560AbXFGEWM (ORCPT ); Thu, 7 Jun 2007 00:22:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752024AbXFGEV7 (ORCPT ); Thu, 7 Jun 2007 00:21:59 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:38719 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751182AbXFGEV5 (ORCPT ); Thu, 7 Jun 2007 00:21:57 -0400 Date: Thu, 7 Jun 2007 09:52:29 +0530 From: "S. P. Prasanna" To: Ian McDonald , Andrew Morton , Andi Kleen Cc: Jim Keniston , Chuck Ebbert , Linux Kernel Mailing List , ananth@in.ibm.com, anil.s.keshavamurthy@intel.com, "David S. Miller" , Patrick Andrieux , DCCP Mailing List , jbeulich@novell.com, systemtap@sources.redhat.com Subject: Re: [PATCH] Kprobes i386 fix for mark ro data Message-ID: <20070607042229.GA9350@in.ibm.com> Reply-To: prasanna@in.ibm.com References: <5640c7e00706061347v42c9ecbahb5354f6687a70a78@mail.gmail.com> <46673B76.2090508@redhat.com> <5640c7e00706061612h62074699wdbd2725654a164@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5640c7e00706061612h62074699wdbd2725654a164@mail.gmail.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6661 Lines: 176 On Thu, Jun 07, 2007 at 11:12:32AM +1200, Ian McDonald wrote: > On 6/7/07, Chuck Ebbert wrote: > >On 06/06/2007 04:47 PM, Ian McDonald wrote: > >> Hi there, > >> > >> We've seen a report of a problem with dccp_probe as shown below. The > >> user has also verified that it occurs in tcp_probe as well. This is on > >> Dave Miller's tree but that currently tracks Linus' tree quite > >> closely. I do note that it is around 2.6.22-rc2 timeframe so there is > >> a possibility fixes may have gone in since. > >> > > > >It faulted when it tried to write the breakpoint instruction into the > >running kernel's executable code. Apparently the kernel code is now marked > >read-only? > > > > > Yes it would appear to be the case as user has CONFIG_DEBUG_RODATA > set. Patrick - can you turn this off and retest? It's under Kernel > Hacking, Write protect kernel read only data structures. > > The list of commits that I see around this are at: > http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git&a=search&h=HEAD&st=commit&s=DEBUG_RODATA > > I suspect it's probably one of the latter ones giving the timing. > > I guess there are a couple of solutions here - either make kprobes > conflict with CONFIG_DEBUG_RODATA so you can do one or the other, or > look into more detail what access kprobes need. > > Ian Ian, Please find the fix as suggested by Andi Kleen for the above stated problem. Thanks Prasanna This patch fixes the problem of page protection introduced by CONFIG_DEBUG_RODATA. CONFIG_DEBUG_RODATA marks the text pages as read-only, hence kprobes is unable to insert breakpoints in the kernel text. This patch overrides the page protection when adding or removing a probe for the i386 architecture. Signed-off-by: Prasanna S P Ack-ed-by: Jim Keniston arch/i386/kernel/kprobes.c | 26 ++++++++++++++++++++++++++ arch/i386/mm/init.c | 2 ++ include/asm-i386/kprobes.h | 12 ++++++++++++ include/asm-i386/pgtable.h | 2 ++ 4 files changed, 42 insertions(+) diff -puN arch/i386/kernel/kprobes.c~kprobes-mark-ro-data-fix-i386 arch/i386/kernel/kprobes.c --- linux-2.6.22-rc2/arch/i386/kernel/kprobes.c~kprobes-mark-ro-data-fix-i386 2007-06-07 09:19:26.000000000 +0530 +++ linux-2.6.22-rc2-prasanna/arch/i386/kernel/kprobes.c 2007-06-07 09:19:26.000000000 +0530 @@ -169,16 +169,42 @@ int __kprobes arch_prepare_kprobe(struct void __kprobes arch_arm_kprobe(struct kprobe *p) { + unsigned long addr = (unsigned long) p->addr; + int page_readonly = 0; + + if (kernel_readonly_text(addr)) { + page_readonly = 1; + change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RWX); + global_flush_tlb(); + } + *p->addr = BREAKPOINT_INSTRUCTION; flush_icache_range((unsigned long) p->addr, (unsigned long) p->addr + sizeof(kprobe_opcode_t)); + + if (page_readonly) { + change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RX); + global_flush_tlb(); + } } void __kprobes arch_disarm_kprobe(struct kprobe *p) { + unsigned long addr = (unsigned long) p->addr; + int page_readonly = 0; + + if (kernel_readonly_text(addr)) { + page_readonly = 1; + change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RWX); + global_flush_tlb(); + } *p->addr = p->opcode; flush_icache_range((unsigned long) p->addr, (unsigned long) p->addr + sizeof(kprobe_opcode_t)); + if (page_readonly) { + change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RX); + global_flush_tlb(); + } } void __kprobes arch_remove_kprobe(struct kprobe *p) diff -puN include/asm-i386/kprobes.h~kprobes-mark-ro-data-fix-i386 include/asm-i386/kprobes.h --- linux-2.6.22-rc2/include/asm-i386/kprobes.h~kprobes-mark-ro-data-fix-i386 2007-06-07 09:19:26.000000000 +0530 +++ linux-2.6.22-rc2-prasanna/include/asm-i386/kprobes.h 2007-06-07 09:19:26.000000000 +0530 @@ -26,6 +26,8 @@ */ #include #include +#include +#include #define __ARCH_WANT_KPROBES_INSN_SLOT @@ -90,4 +92,14 @@ static inline void restore_interrupts(st extern int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data); +extern int kernel_text_is_ro; +static inline int kernel_readonly_text(unsigned long address) +{ + + if (kernel_text_is_ro && ((address >= PFN_ALIGN(_text)) + && (address < PFN_ALIGN(_etext)))) + return 1; + + return 0; +} #endif /* _ASM_KPROBES_H */ diff -puN include/asm-i386/pgtable.h~kprobes-mark-ro-data-fix-i386 include/asm-i386/pgtable.h --- linux-2.6.22-rc2/include/asm-i386/pgtable.h~kprobes-mark-ro-data-fix-i386 2007-06-07 09:19:26.000000000 +0530 +++ linux-2.6.22-rc2-prasanna/include/asm-i386/pgtable.h 2007-06-07 09:19:26.000000000 +0530 @@ -159,6 +159,7 @@ void paging_init(void); extern unsigned long long __PAGE_KERNEL, __PAGE_KERNEL_EXEC; #define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW) #define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW) +#define __PAGE_KERNEL_RWX (__PAGE_KERNEL_EXEC | _PAGE_RW) #define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD) #define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE) #define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE) @@ -167,6 +168,7 @@ extern unsigned long long __PAGE_KERNEL, #define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO) #define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC) #define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX) +#define PAGE_KERNEL_RWX __pgprot(__PAGE_KERNEL_RWX) #define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE) #define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE) #define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC) diff -puN arch/i386/mm/init.c~kprobes-mark-ro-data-fix-i386 arch/i386/mm/init.c --- linux-2.6.22-rc2/arch/i386/mm/init.c~kprobes-mark-ro-data-fix-i386 2007-06-07 09:19:26.000000000 +0530 +++ linux-2.6.22-rc2-prasanna/arch/i386/mm/init.c 2007-06-07 09:19:26.000000000 +0530 @@ -45,6 +45,7 @@ #include #include +int kernel_text_is_ro; unsigned int __VMALLOC_RESERVE = 128 << 20; DEFINE_PER_CPU(struct mmu_gather, mmu_gathers); @@ -807,6 +808,7 @@ void mark_rodata_ro(void) change_page_attr(virt_to_page(start), size >> PAGE_SHIFT, PAGE_KERNEL_RX); printk("Write protecting the kernel text: %luk\n", size >> 10); + kernel_text_is_ro = 1; } start += size; _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/