From ddc65971bb677aa9f6a4c21f76d3133e106f88eb Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Tue, 4 Apr 2023 21:31:48 +0900
Subject: [PATCH] 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>
---
include/uapi/linux/prctl.h | 2 ++
kernel/sys.c | 15 +++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 1312a137f7fb8..b99c0be72577c 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -290,4 +290,6 @@ struct prctl_mm_map {
#define PR_SET_VMA 0x53564d41
# define PR_SET_VMA_ANON_NAME 0
+#define PR_GET_AUXV 0x41555856
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 351de79163020..26c1399e06543 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2388,6 +2388,16 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3,
PR_MDWE_REFUSE_EXEC_GAIN : 0;
}
+static int prctl_get_auxv(void __user *addr, unsigned long len)
+{
+ struct mm_struct *mm = current->mm;
+ unsigned long size = min_t(unsigned long, sizeof(mm->saved_auxv), len);
+
+ if (size && copy_to_user(addr, mm->saved_auxv, size))
+ return -EFAULT;
+ return sizeof(mm->saved_auxv);
+}
+
SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
unsigned long, arg4, unsigned long, arg5)
{
@@ -2518,6 +2528,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
else
return -EINVAL;
break;
+ case PR_GET_AUXV:
+ if (arg4 || arg5)
+ return -EINVAL;
+ error = prctl_get_auxv((void __user *)arg2, arg3);
+ break;
default:
return -EINVAL;
}
--
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