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maccess: always use strict semantics for probe_kernel_read

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Except for historical confusion in the kprobes/uprobes and bpf tracers,
which has been fixed now, there is no good reason to ever allow user
memory accesses from probe_kernel_read.  Switch probe_kernel_read to only
read from kernel memory.

[akpm@linux-foundation.org: update it for "mm, dump_page(): do not crash with invalid mapping pointer"]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200521152301.2587579-17-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Christoph Hellwig
2020-06-08 21:34:50 -07:00
committed by Linus Torvalds
parent 7676fbf21b
commit 98a23609b1
8 changed files with 19 additions and 54 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
mm/maccess.c
View File

@@ -6,36 +6,13 @@
#include <linux/mm.h>
#include <linux/uaccess.h>
static long __probe_kernel_read(void *dst, const void *src, size_t size,
bool strict);
bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size,
bool strict)
bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size)
{
return true;
}
/**
* probe_kernel_read(): safely attempt to read from any location
* @dst: pointer to the buffer that shall take the data
* @src: address to read from
* @size: size of the data chunk
*
* Same as probe_kernel_read_strict() except that for architectures with
* not fully separated user and kernel address spaces this function also works
* for user address tanges.
*
* DO NOT USE THIS FUNCTION - it is broken on architectures with entirely
* separate kernel and user address spaces, and also a bad idea otherwise.
*/
long probe_kernel_read(void *dst, const void *src, size_t size)
{
return __probe_kernel_read(dst, src, size, false);
}
EXPORT_SYMBOL_GPL(probe_kernel_read);
/**
* probe_kernel_read_strict(): safely attempt to read from kernel-space
* probe_kernel_read(): safely attempt to read from kernel-space
* @dst: pointer to the buffer that shall take the data
* @src: address to read from
* @size: size of the data chunk
@@ -48,18 +25,12 @@ EXPORT_SYMBOL_GPL(probe_kernel_read);
* probe_kernel_read() suitable for use within regions where the caller
* already holds mmap_lock, or other locks which nest inside mmap_lock.
*/
long probe_kernel_read_strict(void *dst, const void *src, size_t size)
{
return __probe_kernel_read(dst, src, size, true);
}
static long __probe_kernel_read(void *dst, const void *src, size_t size,
bool strict)
long probe_kernel_read(void *dst, const void *src, size_t size)
{
long ret;
mm_segment_t old_fs = get_fs();
if (!probe_kernel_read_allowed(src, size, strict))
if (!probe_kernel_read_allowed(src, size))
return -EFAULT;
set_fs(KERNEL_DS);
@@ -73,6 +44,7 @@ static long __probe_kernel_read(void *dst, const void *src, size_t size,
return -EFAULT;
return 0;
}
EXPORT_SYMBOL_GPL(probe_kernel_read);
/**
* probe_user_read(): safely attempt to read from a user-space location
@@ -181,7 +153,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
if (unlikely(count <= 0))
return 0;
if (!probe_kernel_read_allowed(unsafe_addr, count, true))
if (!probe_kernel_read_allowed(unsafe_addr, count))
return -EFAULT;
set_fs(KERNEL_DS);