From 0ab32b6f1b88444524e52429fab334ff96683a3f Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@linux-foundation.org>
Date: Thu, 5 Nov 2015 18:46:03 -0800
Subject: [PATCH] uaccess: reimplement probe_kernel_address() using
probe_kernel_read()
probe_kernel_address() is basically the same as the (later added)
probe_kernel_read().
The return value on EFAULT is a bit different: probe_kernel_address()
returns number-of-bytes-not-copied whereas probe_kernel_read() returns
-EFAULT. All callers have been checked, none cared.
probe_kernel_read() can be overridden by the architecture whereas
probe_kernel_address() cannot. parisc, blackfin and um do this, to insert
additional checking. Hence this patch possibly fixes obscure bugs,
although there are only two probe_kernel_address() callsites outside
arch/.
My first attempt involved removing probe_kernel_address() entirely and
converting all callsites to use probe_kernel_read() directly, but that got
tiresome.
This patch shrinks mm/slab_common.o by 218 bytes. For a single
probe_kernel_address() callsite.
Cc: Steven Miao <realmz6@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
arch/arm/mm/alignment.c | 2 +-
arch/powerpc/sysdev/fsl_pci.c | 2 +-
include/linux/uaccess.h | 40 +++++++++--------------------------
mm/maccess.c | 5 +++++
4 files changed, 17 insertions(+), 32 deletions(-)
diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index 00b7f7de28a182..7d5f4c736a16b4 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -803,7 +803,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
}
}
} else {
- fault = probe_kernel_address(instrptr, instr);
+ fault = probe_kernel_address((void *)instrptr, instr);
instr = __mem_to_opcode_arm(instr);
}
diff --git a/arch/powerpc/sysdev/fsl_pci.c b/arch/powerpc/sysdev/fsl_pci.c
index ebc1f412cf4921..13b9bcf5485e5f 100644
--- a/arch/powerpc/sysdev/fsl_pci.c
+++ b/arch/powerpc/sysdev/fsl_pci.c
@@ -999,7 +999,7 @@ int fsl_pci_mcheck_exception(struct pt_regs *regs)
ret = get_user(regs->nip, &inst);
pagefault_enable();
} else {
- ret = probe_kernel_address(regs->nip, inst);
+ ret = probe_kernel_address((void *)regs->nip, inst);
}
if (mcheck_handle_load(regs, inst)) {
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index d6f2c2c5b04337..558129af828a7e 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -75,36 +75,6 @@ static inline unsigned long __copy_from_user_nocache(void *to,
#endif /* ARCH_HAS_NOCACHE_UACCESS */
-/**
- * probe_kernel_address(): safely attempt to read from a location
- * @addr: address to read from - its type is type typeof(retval)*
- * @retval: read into this variable
- *
- * Safely read from address @addr into variable @revtal. If a kernel fault
- * happens, handle that and return -EFAULT.
- * We ensure that the __get_user() is executed in atomic context so that
- * do_page_fault() doesn't attempt to take mmap_sem. This makes
- * probe_kernel_address() suitable for use within regions where the caller
- * already holds mmap_sem, or other locks which nest inside mmap_sem.
- * This must be a macro because __get_user() needs to know the types of the
- * args.
- *
- * We don't include enough header files to be able to do the set_fs(). We
- * require that the probe_kernel_address() caller will do that.
- */
-#define probe_kernel_address(addr, retval) \
- ({ \
- long ret; \
- mm_segment_t old_fs = get_fs(); \
- \
- set_fs(KERNEL_DS); \
- pagefault_disable(); \
- ret = __copy_from_user_inatomic(&(retval), (__force typeof(retval) __user *)(addr), sizeof(retval)); \
- pagefault_enable(); \
- set_fs(old_fs); \
- ret; \
- })
-
/*
* probe_kernel_read(): safely attempt to read from a location
* @dst: pointer to the buffer that shall take the data
@@ -131,4 +101,14 @@ extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size
extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
+/**
+ * probe_kernel_address(): safely attempt to read from a location
+ * @addr: address to read from
+ * @retval: read into this variable
+ *
+ * Returns 0 on success, or -EFAULT.
+ */
+#define probe_kernel_address(addr, retval) \
+ probe_kernel_read(&retval, addr, sizeof(retval))
+
#endif /* __LINUX_UACCESS_H__ */
diff --git a/mm/maccess.c b/mm/maccess.c
index 34fe24759ed1f3..1b13638d238d51 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -13,6 +13,11 @@
*
* 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_kernel_read() suitable for use within regions where the caller
+ * already holds mmap_sem, or other locks which nest inside mmap_sem.
*/
long __weak probe_kernel_read(void *dst, const void *src, size_t size)
--
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