Messages in this thread Patch in this message | | | From | David Howells <> | Subject | [PATCH] NOMMU: Permit ptrace to ignore non-PROT_WRITE VMAs in NOMMU mode | Date | Thu, 31 Aug 2006 21:24:29 +0100 |
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From: David Howells <dhowells@redhat.com>
Permit ptrace to modify a section that's non-shared but is marked unwritable, such as is obtained by mapping the text segment of an ELF-FDPIC executable binary with into a binary that's being ptraced[*].
[*] Under NOMMU conditions ptrace causes read-only MAP_PRIVATE mmaps to become totally private copies because if a private mapping was actually shared then the debugging setting breakpoints in it would potentially crash other processes.
This is done by using the VM_MAYWRITE flag rather than the VM_WRITE flag when deciding whether to permit a write.
Without this patch a debugger can't set breakpoints in the mapped text sections of executables that are mapped read-only private, even if the mmap() syscall has taken a private copy because PT_PTRACED is set.
In addition, VM_MAYREAD is used instead of VM_READ for similar reasons.
Signed-Off-By: David Howells <dhowells@redhat.com> ---
mm/nommu.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/nommu.c b/mm/nommu.c index 51e17b9..9d57c2a 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1234,9 +1234,9 @@ int access_process_vm(struct task_struct len = vma->vm_end - addr; /* only read or write mappings where it is permitted */ - if (write && vma->vm_flags & VM_WRITE) + if (write && vma->vm_flags & VM_MAYWRITE) len -= copy_to_user((void *) addr, buf, len); - else if (!write && vma->vm_flags & VM_READ) + else if (!write && vma->vm_flags & VM_MAYREAD) len -= copy_from_user(buf, (void *) addr, len); else len = 0; - 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/
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