From: Will Deacon Date: Sat, 19 Jan 2019 21:56:05 +0000 (+0000) Subject: x86: uaccess: Inhibit speculation past access_ok() in user_access_begin() X-Git-Tag: v5.4-rc1~1757 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=6e693b3ffecb0b478c7050b44a4842854154f715;p=platform%2Fkernel%2Flinux-rpi.git x86: uaccess: Inhibit speculation past access_ok() in user_access_begin() 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 --- diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index a77445d..780f2b4 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -711,7 +711,7 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t { if (unlikely(!access_ok(ptr,len))) return 0; - __uaccess_begin(); + __uaccess_begin_nospec(); return 1; } #define user_access_begin(a,b) user_access_begin(a,b)