From: Will Deacon <will.deacon@xxxxxxx>
commit c2f0ad4fc089cff81cef6a13d04b399980ecbfcc upstream.
A mispredicted conditional call to set_fs could result in the wrong
addr_limit being forwarded under speculation to a subsequent access_ok
check, potentially forming part of a spectre-v1 attack using uaccess
routines.
This patch prevents this forwarding from taking place, but putting heavy
barriers in set_fs after writing the addr_limit.
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 75363d723262..fc11c50af558 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -62,6 +62,13 @@ extern int fixup_exception(struct pt_regs *regs);
static inline void set_fs(mm_segment_t fs)
{
current_thread_info()->addr_limit = fs;
+
+ /*
+ * Prevent a mispredicted conditional call to set_fs from forwarding
+ * the wrong address limit to access_ok under speculation.
+ */
+ dsb(nsh);
+ isb();
}
#define segment_eq(a, b) ((a) == (b))
--
2.21.0.rc0.269.g1a574e7a288b
