[PATCH v2 1/2] mm: add probe_user_read()
From: Christophe Leroy <hidden>
Date: 2019-01-08 07:37:49
In powerpc code, 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(), this patch adds
probe_user_read().
probe_user_read() does the same as probe_kernel_read() but
first checks that it is really a user address.
Signed-off-by: Christophe Leroy <redacted>
---
v2: Added "Returns:" comment and removed probe_user_address()
Changes since RFC: Made a static inline function instead of weak function as recommended by Kees.
include/linux/uaccess.h | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 37b226e8df13..07f4f0ed69bc 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h@@ -263,6 +263,40 @@ 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 + * + * Returns: 0 on success, -EFAULT on error. + * + * 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(src, size)) + return -EFAULT; + + pagefault_disable(); + ret = __copy_from_user_inatomic(dst, src, size); + pagefault_enable(); + + return ret ? -EFAULT : 0; +} +#endif + #ifndef user_access_begin #define user_access_begin(ptr,len) access_ok(ptr, len) #define user_access_end() do { } while (0)
--
2.13.3