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Message-Id: <20200519134449.1466624-13-hch@lst.de>
Date: Tue, 19 May 2020 15:44:41 +0200
From: Christoph Hellwig <hch@....de>
To: x86@...nel.org, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Masami Hiramatsu <mhiramat@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-parisc@...r.kernel.org, linux-um@...ts.infradead.org,
netdev@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 12/20] maccess: remove strncpy_from_unsafe
All three callers really should try the explicit kernel or user copies.
Switch them to try a user copy if the address is smaller than TASK_SIZE
and the architecture has non-overlapping address ranges, or a kernel copy
otherwise.
Signed-off-by: Christoph Hellwig <hch@....de>
---
include/linux/uaccess.h | 1 -
kernel/trace/bpf_trace.c | 23 +++++++++++++++-------
kernel/trace/trace_kprobe.c | 8 +++++++-
mm/maccess.c | 39 +------------------------------------
4 files changed, 24 insertions(+), 47 deletions(-)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 7cfc10eb09c60..28944a14e0534 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -311,7 +311,6 @@ extern long probe_user_read(void *dst, const void __user *src, size_t size);
extern long notrace probe_kernel_write(void *dst, const void *src, size_t size);
extern long notrace probe_user_write(void __user *dst, const void *src, size_t size);
-extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr,
long count);
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 9d4080590f711..bab9b8a175cb0 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -226,12 +226,14 @@ static __always_inline int
bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr,
const bool compat)
{
+ const void __user *user_ptr = (__force const void __user *)unsafe_ptr;
int ret = security_locked_down(LOCKDOWN_BPF_READ);
if (unlikely(ret < 0))
- goto out;
+ goto fail;
+
/*
- * The strncpy_from_unsafe_*() call will likely not fill the entire
+ * The strncpy_from_*_nofault() calls will likely not fill the entire
* buffer, but that's okay in this circumstance as we're probing
* arbitrary memory anyway similar to bpf_probe_read_*() and might
* as well probe the stack. Thus, memory is explicitly cleared
@@ -239,11 +241,17 @@ bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr,
* code altogether don't copy garbage; otherwise length of string
* is returned that can be used for bpf_perf_event_output() et al.
*/
- ret = compat ? strncpy_from_unsafe(dst, unsafe_ptr, size) :
- strncpy_from_kernel_nofault(dst, unsafe_ptr, size);
+ if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) &&
+ compat && (unsigned long)unsafe_ptr < TASK_SIZE)
+ ret = strncpy_from_user_nofault(dst, user_ptr, size);
+ else
+ ret = strncpy_from_kernel_nofault(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
-out:
- memset(dst, 0, size);
+ goto fail;
+
+ return 0;
+fail:
+ memset(dst, 0, size);
return ret;
}
@@ -331,7 +339,8 @@ static void bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
switch (fmt_ptype) {
case 's':
#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
- strncpy_from_unsafe(buf, unsafe_ptr, bufsz);
+ if (strncpy_from_kernel_nofault(buf, unsafe_ptr, bufsz) == 0)
+ strncpy_from_user_nofault(buf, user_ptr, bufsz);
break;
#endif
case 'k':
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 4325f9e7fadaa..2f6737cc53e6c 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1244,7 +1244,13 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
* Try to get string again, since the string can be changed while
* probing.
*/
- ret = strncpy_from_unsafe(__dest, (void *)addr, maxlen);
+ if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) &&
+ addr < TASK_SIZE) {
+ ret = strncpy_from_user_nofault(__dest, (void __user *)addr,
+ maxlen);
+ } else {
+ ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
+ }
if (ret >= 0)
*(u32 *)dest = make_data_loc(ret, __dest - base);
diff --git a/mm/maccess.c b/mm/maccess.c
index 483a933b7d241..3d85e48013e6b 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -8,8 +8,6 @@
static long __probe_kernel_read(void *dst, const void *src, size_t size,
bool strict);
-static long __strncpy_from_unsafe(char *dst, const void *unsafe_addr,
- long count, bool strict);
bool __weak probe_kernel_read_allowed(void *dst, const void *unsafe_src,
size_t size, bool strict)
@@ -156,35 +154,6 @@ long probe_user_write(void __user *dst, const void *src, size_t size)
return 0;
}
-/**
- * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.
- * @dst: Destination address, in kernel space. This buffer must be at
- * least @count bytes long.
- * @unsafe_addr: Unsafe address.
- * @count: Maximum number of bytes to copy, including the trailing NUL.
- *
- * Copies a NUL-terminated string from unsafe address to kernel buffer.
- *
- * On success, returns the length of the string INCLUDING the trailing NUL.
- *
- * If access fails, returns -EFAULT (some data may have been copied
- * and the trailing NUL added).
- *
- * If @count is smaller than the length of the string, copies @count-1 bytes,
- * sets the last byte of @dst buffer to NUL and returns @count.
- *
- * Same as strncpy_from_kernel_nofault() 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 strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
-{
- return __strncpy_from_unsafe(dst, unsafe_addr, count, false);
-}
-
/**
* strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
* address.
@@ -204,12 +173,6 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
* sets the last byte of @dst buffer to NUL and returns @count.
*/
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
-{
- return __strncpy_from_unsafe(dst, unsafe_addr, count, true);
-}
-
-static long __strncpy_from_unsafe(char *dst, const void *unsafe_addr,
- long count, bool strict)
{
mm_segment_t old_fs = get_fs();
const void *src = unsafe_addr;
@@ -217,7 +180,7 @@ static long __strncpy_from_unsafe(char *dst, const void *unsafe_addr,
if (unlikely(count <= 0))
return 0;
- if (!probe_kernel_read_allowed(dst, unsafe_addr, count, strict))
+ if (!probe_kernel_read_allowed(dst, unsafe_addr, count, true))
return -EFAULT;
set_fs(KERNEL_DS);
--
2.26.2
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