On Thu, Jun 07, 2007 at 11:12:32AM +1200, Ian McDonald wrote:
> On 6/7/07, Chuck Ebbert <[EMAIL PROTECTED]> 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<[EMAIL PROTECTED]>
Ack-ed-by: Jim Keniston <[EMAIL PROTECTED]>
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 <linux/types.h>
#include <linux/ptrace.h>
+#include <linux/pfn.h>
+#include <asm-generic/sections.h>
#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 <asm/sections.h>
#include <asm/paravirt.h>
+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;
_
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