INCIDENT OCCURRED WHILE CONTACT (C) WAS BACKING SRX DOWN THE APPROX 40 DEGREE UPSLOPE 100' LONG DRIVEWAY CURVED AT BOTTOM. SURFACES WERE DRY & IT WAS SUNNY. C PURCHASED SRX NEW (NAVIGATION, DRIVER AWARENESS & DRIVER ASSIST) IN LATE 12/13. C &/OR SPOUSE HAVE BACKED SRX DOWN DRIVEWAY WITHOUT INCIDENT 100 PLUS TIMES. C & SPOUSE ENTERED SRX, ADJUSTED SEATS & MIRROR, & BUCKLED SEAT BELTS. C DEPRESSED BRAKE PEDAL & PUSHED START BUTTON. WHILE RETAINING PRESSURE ON BRAKE, C SHIFTED TRANSMISSION SELECTOR INTO R, 'REVERSE.' THE BACK-UP CAMERA DISPLAY APPEARED. IMMEDIATELY, SRX BEGAN TO ROLL DOWN DRIVEWAY. ROLLING CONTINUED DESPITE INCREASING BRAKE PEDAL PRESSURE EXERTED. C WAS STANDING ON BRAKE PEDAL TO GET SRX TO RESPOND TO FULL STOP. VIEWING THE BACK-UP CAMERA DISPLAY, C ATTEMPTED TO STEER SRX SO AS TO AVOID ENTERING STREET. SRX WAS STOPPED BY IMPACTING RETAINING WALL ON LEFT SIDE OF DRIVEWAY. ONCE SRX HAD STOPPED, C (WITH BRAKE PEDAL STILL DEPRESSED) WAS ABLE TO SHIFT GEARS & MOVE SRX FROM DRIVEWAY. C TESTED SRX BY DRIVING FORWARDS & BRAKING & NOTED NO ISSUES. SRX WAS DEALER INSPECTED. DEALER INDICATED THAT IT: "COULD NOT DUPLICATE CONCERN. CHECKED FOR BULLETINS, NO RELATED BULLETINS. INSPECTED BRAKE FLUID FOR LEAKS, NO LEAKS. NO STORED DTC'S." RE: SRX'S HILL START ASSIST FEATURE, WHICH HOLDS SRX FOR MAXIMUM OF TWO SECS SO DRIVER MAY MOVE FROM BRAKE TO ACCELERATOR WITHOUT RISK OF ROLLING - FEATURE DOES NOT FUNCTION. DEALER VERBALLY STATED THAT ON STEEP HILLS, SRX SHOULD BE DRIVEN WI