4.20-stable review patch. If anyone has any objections, please let me know.
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From: Andy Lutomirski luto@kernel.org
commit 2a418cf3f5f1caf911af288e978d61c9844b0695 upstream.
When calling __put_user(foo(), ptr), the __put_user() macro would call foo() in between __uaccess_begin() and __uaccess_end(). If that code were buggy, then those bugs would be run without SMAP protection.
Fortunately, there seem to be few instances of the problem in the kernel. Nevertheless, __put_user() should be fixed to avoid doing this. Therefore, evaluate __put_user()'s argument before setting AC.
This issue was noticed when an objtool hack by Peter Zijlstra complained about genregs_get() and I compared the assembly output to the C source.
[ bp: Massage commit message and fixed up whitespace. ]
Fixes: 11f1a4b9755f ("x86: reorganize SMAP handling in user space accesses") Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Brian Gerst brgerst@gmail.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20190225125231.845656645@infradead.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -293,8 +293,7 @@ do { \ __put_user_asm(x, ptr, retval, "l", "k", "ir", errret); \ break; \ case 8: \ - __put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval, \ - errret); \ + __put_user_asm_u64(x, ptr, retval, errret); \ break; \ default: \ __put_user_bad(); \ @@ -440,8 +439,10 @@ do { \ #define __put_user_nocheck(x, ptr, size) \ ({ \ int __pu_err; \ + __typeof__(*(ptr)) __pu_val; \ + __pu_val = x; \ __uaccess_begin(); \ - __put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \ + __put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT);\ __uaccess_end(); \ __builtin_expect(__pu_err, 0); \ })