From: Will Deacon will.deacon@arm.com
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 julien.thierry@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Cc: Miles Chen miles.chen@mediatek.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/uaccess.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -717,7 +717,7 @@ static __must_check inline bool user_acc { if (unlikely(!access_ok(type, ptr, len))) return 0; - __uaccess_begin(); + __uaccess_begin_nospec(); return 1; }