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Date: Fri, 9 Feb 2018 14:39:31 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <ak@...ux.intel.com>, Dan Williams <dan.j.williams@...el.com>, Thomas Gleixner <tglx@...utronix.de>, linux-arch@...r.kernel.org, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, Al Viro <viro@...iv.linux.org.uk>, alan@...ux.intel.com, David Woodhouse <dwmw@...zon.co.uk> Subject: [PATCH 4.9 62/92] x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dan Williams <dan.j.williams@...el.com> (cherry picked from commit 304ec1b050310548db33063e567123fae8fd0301) Quoting Linus: I do think that it would be a good idea to very expressly document the fact that it's not that the user access itself is unsafe. I do agree that things like "get_user()" want to be protected, but not because of any direct bugs or problems with get_user() and friends, but simply because get_user() is an excellent source of a pointer that is obviously controlled from a potentially attacking user space. So it's a prime candidate for then finding _subsequent_ accesses that can then be used to perturb the cache. __uaccess_begin_nospec() covers __get_user() and copy_from_iter() where the limit check is far away from the user pointer de-reference. In those cases a barrier_nospec() prevents speculation with a potential pointer to privileged memory. uaccess_try_nospec covers get_user_try. Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org> Suggested-by: Andi Kleen <ak@...ux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@...el.com> Signed-off-by: Thomas Gleixner <tglx@...utronix.de> Cc: linux-arch@...r.kernel.org Cc: Kees Cook <keescook@...omium.org> Cc: kernel-hardening@...ts.openwall.com Cc: gregkh@...uxfoundation.org Cc: Al Viro <viro@...iv.linux.org.uk> Cc: alan@...ux.intel.com Link: https://lkml.kernel.org/r/151727416953.33451.10508284228526170604.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: David Woodhouse <dwmw@...zon.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- arch/x86/include/asm/uaccess.h | 6 +++--- arch/x86/include/asm/uaccess_32.h | 12 ++++++------ arch/x86/include/asm/uaccess_64.h | 12 ++++++------ arch/x86/lib/usercopy_32.c | 4 ++-- 4 files changed, 17 insertions(+), 17 deletions(-) --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -437,7 +437,7 @@ do { \ ({ \ int __gu_err; \ __inttype(*(ptr)) __gu_val; \ - __uaccess_begin(); \ + __uaccess_begin_nospec(); \ __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \ __uaccess_end(); \ (x) = (__force __typeof__(*(ptr)))__gu_val; \ @@ -547,7 +547,7 @@ struct __large_struct { unsigned long bu * get_user_ex(...); * } get_user_catch(err) */ -#define get_user_try uaccess_try +#define get_user_try uaccess_try_nospec #define get_user_catch(err) uaccess_catch(err) #define get_user_ex(x, ptr) do { \ @@ -582,7 +582,7 @@ extern void __cmpxchg_wrong_size(void) __typeof__(ptr) __uval = (uval); \ __typeof__(*(ptr)) __old = (old); \ __typeof__(*(ptr)) __new = (new); \ - __uaccess_begin(); \ + __uaccess_begin_nospec(); \ switch (size) { \ case 1: \ { \ --- a/arch/x86/include/asm/uaccess_32.h +++ b/arch/x86/include/asm/uaccess_32.h @@ -102,17 +102,17 @@ __copy_from_user(void *to, const void __ switch (n) { case 1: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u8 *)to, from, 1, ret, 1); __uaccess_end(); return ret; case 2: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u16 *)to, from, 2, ret, 2); __uaccess_end(); return ret; case 4: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u32 *)to, from, 4, ret, 4); __uaccess_end(); return ret; @@ -130,17 +130,17 @@ static __always_inline unsigned long __c switch (n) { case 1: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u8 *)to, from, 1, ret, 1); __uaccess_end(); return ret; case 2: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u16 *)to, from, 2, ret, 2); __uaccess_end(); return ret; case 4: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_size(*(u32 *)to, from, 4, ret, 4); __uaccess_end(); return ret; --- a/arch/x86/include/asm/uaccess_64.h +++ b/arch/x86/include/asm/uaccess_64.h @@ -59,31 +59,31 @@ int __copy_from_user_nocheck(void *dst, return copy_user_generic(dst, (__force void *)src, size); switch (size) { case 1: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u8 *)dst, (u8 __user *)src, ret, "b", "b", "=q", 1); __uaccess_end(); return ret; case 2: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u16 *)dst, (u16 __user *)src, ret, "w", "w", "=r", 2); __uaccess_end(); return ret; case 4: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u32 *)dst, (u32 __user *)src, ret, "l", "k", "=r", 4); __uaccess_end(); return ret; case 8: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u64 *)dst, (u64 __user *)src, ret, "q", "", "=r", 8); __uaccess_end(); return ret; case 10: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u64 *)dst, (u64 __user *)src, ret, "q", "", "=r", 10); if (likely(!ret)) @@ -93,7 +93,7 @@ int __copy_from_user_nocheck(void *dst, __uaccess_end(); return ret; case 16: - __uaccess_begin(); + __uaccess_begin_nospec(); __get_user_asm(*(u64 *)dst, (u64 __user *)src, ret, "q", "", "=r", 16); if (likely(!ret)) --- a/arch/x86/lib/usercopy_32.c +++ b/arch/x86/lib/usercopy_32.c @@ -570,7 +570,7 @@ do { \ unsigned long __copy_to_user_ll(void __user *to, const void *from, unsigned long n) { - __uaccess_begin(); + __uaccess_begin_nospec(); if (movsl_is_ok(to, from, n)) __copy_user(to, from, n); else @@ -627,7 +627,7 @@ EXPORT_SYMBOL(__copy_from_user_ll_nocach unsigned long __copy_from_user_ll_nocache_nozero(void *to, const void __user *from, unsigned long n) { - __uaccess_begin(); + __uaccess_begin_nospec(); #ifdef CONFIG_X86_INTEL_USERCOPY if (n > 64 && static_cpu_has(X86_FEATURE_XMM2)) n = __copy_user_intel_nocache(to, from, n);
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