arm64: ssbd: Introduce thread flag to control userspace mitigation

In order to allow userspace to be mitigated on demand, let's
introduce a new thread flag that prevents the mitigation from
being turned off when exiting to userspace, and doesn't turn
it on on entry into the kernel (with the assumption that the
mitigation is always enabled in the kernel itself).

This will be used by a prctl interface introduced in a later
patch.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 740aa03c5f0dc8bd6ead32b57453e4537895f56e..cbcf11b5e6377f0b87a59921d7154c1d64fccf39 100644 (file)
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -94,6 +94,7 @@ void arch_release_task_struct(struct task_struct *tsk);
 #define TIF_32BIT              22      /* 32bit process */
 #define TIF_SVE                        23      /* Scalable Vector Extension in use */
 #define TIF_SVE_VL_INHERIT     24      /* Inherit sve_vl_onexec across exec */
+#define TIF_SSBD               25      /* Wants SSB mitigation */
 
 #define _TIF_SIGPENDING                (1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED      (1 << TIF_NEED_RESCHED)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e6f6e2339b22f36cc9a03313bc2e77df07a15be0..28ad8799406ffdf6d6e11c336305f1f1ad9ea303 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -147,6 +147,8 @@ alternative_cb      arm64_enable_wa2_handling
 alternative_cb_end
        ldr_this_cpu    \tmp2, arm64_ssbd_callback_required, \tmp1
        cbz     \tmp2, \targ
+       ldr     \tmp2, [tsk, #TSK_TI_FLAGS]
+       tbnz    \tmp2, #TIF_SSBD, \targ
        mov     w0, #ARM_SMCCC_ARCH_WORKAROUND_2
        mov     w1, #\state
 alternative_cb arm64_update_smccc_conduit