From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-mm@kvack.org
Subject: [PATCH 1/2] mm: add probe_user_read() and probe_user_address()
Date: Mon, 3 Dec 2018 17:06:42 +0000 (UTC) [thread overview]
Message-ID: <dd9ef91add7fcf5a9e369dde322b1822e90eb218.1543811917.git.christophe.leroy@c-s.fr> (raw)
In the powerpc, there are several places implementing safe
access to user data. This is sometimes implemented using
probe_kernel_address() with additional access_ok() verification,
sometimes with get_user() enclosed in a pagefault_disable()/enable()
pair, etc... :
show_user_instructions()
bad_stack_expansion()
p9_hmi_special_emu()
fsl_pci_mcheck_exception()
read_user_stack_64()
read_user_stack_32() on PPC64
read_user_stack_32() on PPC32
power_pmu_bhrb_to()
In the same spirit as probe_kernel_read() and probe_kernel_address(),
this patch adds probe_user_read() and probe_user_address().
probe_user_read() does the same as probe_kernel_read() but
first checks that it is really a user address.
probe_user_address() is a shortcut to probe_user_read()
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
Changes since RFC: Made a static inline function instead of weak function as recommended by Kees.
include/linux/uaccess.h | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index efe79c1cdd47..83ea8aefca75 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -266,6 +266,48 @@ extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
#define probe_kernel_address(addr, retval) \
probe_kernel_read(&retval, addr, sizeof(retval))
+/**
+ * probe_user_read(): safely attempt to read from a user location
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from
+ * @size: size of the data chunk
+ *
+ * Safely read from address @src to the buffer at @dst. If a kernel fault
+ * happens, handle that and return -EFAULT.
+ *
+ * We ensure that the copy_from_user is executed in atomic context so that
+ * do_page_fault() doesn't attempt to take mmap_sem. This makes
+ * probe_user_read() suitable for use within regions where the caller
+ * already holds mmap_sem, or other locks which nest inside mmap_sem.
+ */
+
+#ifndef probe_user_read
+static __always_inline long probe_user_read(void *dst, const void __user *src,
+ size_t size)
+{
+ long ret;
+
+ if (!access_ok(VERIFY_READ, src, size))
+ return -EFAULT;
+
+ pagefault_disable();
+ ret = __copy_from_user_inatomic(dst, src, size);
+ pagefault_enable();
+
+ return ret ? -EFAULT : 0;
+}
+#endif
+
+/**
+ * probe_user_address(): safely attempt to read from a user location
+ * @addr: address to read from
+ * @retval: read into this variable
+ *
+ * Returns 0 on success, or -EFAULT.
+ */
+#define probe_user_address(addr, retval) \
+ probe_user_read(&(retval), addr, sizeof(retval))
+
#ifndef user_access_begin
#define user_access_begin() do { } while (0)
#define user_access_end() do { } while (0)
--
2.13.3
next reply other threads:[~2018-12-03 17:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 17:06 Christophe Leroy [this message]
2018-12-03 17:06 ` [PATCH 2/2] powerpc: use probe_user_read() and probe_user_address() Christophe Leroy
2018-12-03 17:53 ` [PATCH 1/2] mm: add " Mike Rapoport
2018-12-04 8:42 ` Michael Ellerman
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