[PATCH] NOMMU: Permit ptrace to ignore non-PROT_WRITE VMAs in NOMMU mode
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> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -1258,9 +1258,9 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
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len = vma->vm_end - addr;
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/* only read or write mappings where it is permitted */
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if (write && vma->vm_flags & VM_WRITE)
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if (write && vma->vm_flags & VM_MAYWRITE)
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len -= copy_to_user((void *) addr, buf, len);
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else if (!write && vma->vm_flags & VM_READ)
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else if (!write && vma->vm_flags & VM_MAYREAD)
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len -= copy_from_user(buf, (void *) addr, len);
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else
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len = 0;
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