| Message ID | 0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] mm: add probe_user_read() | expand |
On Tue, Jan 08, 2019 at 07:37:44AM +0000, Christophe Leroy wrote: > 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 <christophe.leroy@c-s.fr> > --- > 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. Nit: please put the "Returns:" comment after the description, otherwise kernel-doc considers it a part of the elaborate description. > + * > + * 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 >
On Tue, 8 Jan 2019 07:37:44 +0000 (UTC) Christophe Leroy <christophe.leroy@c-s.fr> wrote: > 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. > > ... > > --- 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 Why was the __always_inline needed? This function is pretty large. Why is it inlined?
Le 08/01/2019 à 20:48, Andrew Morton a écrit : > On Tue, 8 Jan 2019 07:37:44 +0000 (UTC) Christophe Leroy <christophe.leroy@c-s.fr> wrote: > >> 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. >> >> ... >> >> --- 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 > > Why was the __always_inline needed? > > This function is pretty large. Why is it inlined? > Kees told to do that way, see https://patchwork.ozlabs.org/patch/986848/ Christophe
On Tue, Jan 8, 2019 at 1:11 PM Christophe Leroy <christophe.leroy@c-s.fr> wrote: > > > > Le 08/01/2019 à 20:48, Andrew Morton a écrit : > > On Tue, 8 Jan 2019 07:37:44 +0000 (UTC) Christophe Leroy <christophe.leroy@c-s.fr> wrote: > > > >> 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. > >> > >> ... > >> > >> --- 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 > > > > Why was the __always_inline needed? > > > > This function is pretty large. Why is it inlined? > > > > Kees told to do that way, see https://patchwork.ozlabs.org/patch/986848/ Yeah, I'd like to make sure we can plumb the size checks down into the user copy primitives.
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)
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 <christophe.leroy@c-s.fr> --- 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(+)