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prctl: add PR_GET_AUXV to copy auxv to userspace
If a library wants to get information from auxv (for instance, AT_HWCAP/AT_HWCAP2), it has a few options, none of them perfectly reliable or ideal: - Be main or the pre-main startup code, and grub through the stack above main. Doesn't work for a library. - Call libc getauxval. Not ideal for libraries that are trying to be libc-independent and/or don't otherwise require anything from other libraries. - Open and read /proc/self/auxv. Doesn't work for libraries that may run in arbitrarily constrained environments that may not have /proc mounted (e.g. libraries that might be used by an init program or a container setup tool). - Assume you're on the main thread and still on the original stack, and try to walk the stack upwards, hoping to find auxv. Extremely bad idea. - Ask the caller to pass auxv in for you. Not ideal for a user-friendly library, and then your caller may have the same problem. Add a prctl that copies current->mm->saved_auxv to a userspace buffer. Link: https://lkml.kernel.org/r/d81864a7f7f43bca6afa2a09fc2e850e4050ab42.1680611394.git.josh@joshtriplett.org Signed-off-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -290,4 +290,6 @@ struct prctl_mm_map {
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#define PR_SET_VMA 0x53564d41
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# define PR_SET_VMA_ANON_NAME 0
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#define PR_GET_AUXV 0x41555856
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#endif /* _LINUX_PRCTL_H */
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15
kernel/sys.c
15
kernel/sys.c
@ -2388,6 +2388,16 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3,
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PR_MDWE_REFUSE_EXEC_GAIN : 0;
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}
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static int prctl_get_auxv(void __user *addr, unsigned long len)
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{
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struct mm_struct *mm = current->mm;
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unsigned long size = min_t(unsigned long, sizeof(mm->saved_auxv), len);
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if (size && copy_to_user(addr, mm->saved_auxv, size))
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return -EFAULT;
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return sizeof(mm->saved_auxv);
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}
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SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
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unsigned long, arg4, unsigned long, arg5)
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{
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@ -2518,6 +2528,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
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else
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return -EINVAL;
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break;
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case PR_GET_AUXV:
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if (arg4 || arg5)
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return -EINVAL;
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error = prctl_get_auxv((void __user *)arg2, arg3);
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break;
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default:
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return -EINVAL;
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}
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