From b46395f443d61ec34cd9e42d05cae1eebbd4c31a Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Sat, 19 Jan 2019 21:56:05 +0000 Subject: [PATCH] x86: uaccess: Inhibit speculation past access_ok() in user_access_begin() commit 6e693b3ffecb0b478c7050b44a4842854154f715 upstream. Commit 594cc251fdd0 ("make 'user_access_begin()' do 'access_ok()'") makes the access_ok() check part of the user_access_begin() preceding a series of 'unsafe' accesses. This has the desirable effect of ensuring that all 'unsafe' accesses have been range-checked, without having to pick through all of the callsites to verify whether the appropriate checking has been made. However, the consolidated range check does not inhibit speculation, so it is still up to the caller to ensure that they are not susceptible to any speculative side-channel attacks for user addresses that ultimately fail the access_ok() check. This is an oversight, so use __uaccess_begin_nospec() to ensure that speculation is inhibited until the access_ok() check has passed. Reported-by: Julien Thierry Signed-off-by: Will Deacon Signed-off-by: Linus Torvalds Cc: Miles Chen Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/uaccess.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index d871e424fa50..82b0ff6cac97 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -717,7 +717,7 @@ static __must_check inline bool user_access_begin(int type, { if (unlikely(!access_ok(type, ptr, len))) return 0; - __uaccess_begin(); + __uaccess_begin_nospec(); return 1; }