ARM: signal: copy registers using __copy_from_user()

Commit c32cd419d6650e42b9cdebb83c672ec945e6bd7e upstream.

__get_user_error() is used as a fast accessor to make copying structure
members in the signal handling path as efficient as possible.  However,
with software PAN and the recent Spectre variant 1, the efficiency is
reduced as these are no longer fast accessors.

In the case of software PAN, it has to switch the domain register around
each access, and with Spectre variant 1, it would have to repeat the
access_ok() check for each access.

It becomes much more efficient to use __copy_from_user() instead, so
let's use this for the ARM integer registers.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David A. Long <dave.long@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 7b8f2141427bda172899bfe8ae5113367163af47..a592bc0287f86761aef8a3f0f201f265a3b79e30 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -141,6 +141,7 @@ struct rt_sigframe {
 
 static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
 {
+       struct sigcontext context;
        struct aux_sigframe __user *aux;
        sigset_t set;
        int err;
@@ -149,23 +150,26 @@ static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
        if (err == 0)
                set_current_blocked(&set);
 
-       __get_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
-       __get_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
-       __get_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
-       __get_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
-       __get_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
-       __get_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
-       __get_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
-       __get_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
-       __get_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
-       __get_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
-       __get_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
-       __get_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
-       __get_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
-       __get_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
-       __get_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
-       __get_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
-       __get_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);
+       err |= __copy_from_user(&context, &sf->uc.uc_mcontext, sizeof(context));
+       if (err == 0) {
+               regs->ARM_r0 = context.arm_r0;
+               regs->ARM_r1 = context.arm_r1;
+               regs->ARM_r2 = context.arm_r2;
+               regs->ARM_r3 = context.arm_r3;
+               regs->ARM_r4 = context.arm_r4;
+               regs->ARM_r5 = context.arm_r5;
+               regs->ARM_r6 = context.arm_r6;
+               regs->ARM_r7 = context.arm_r7;
+               regs->ARM_r8 = context.arm_r8;
+               regs->ARM_r9 = context.arm_r9;
+               regs->ARM_r10 = context.arm_r10;
+               regs->ARM_fp = context.arm_fp;
+               regs->ARM_ip = context.arm_ip;
+               regs->ARM_sp = context.arm_sp;
+               regs->ARM_lr = context.arm_lr;
+               regs->ARM_pc = context.arm_pc;
+               regs->ARM_cpsr = context.arm_cpsr;
+       }
 
        err |= !valid_user_regs(regs);