commit 8e2906245f1e3b0d027169d9f2e55ce0548cb96e upstream.
In order for the kernel to protect itself, let's call the SSBD mitigation implemented by the higher exception level (either hypervisor or firmware) on each transition between userspace and kernel.
We must take the PSCI conduit into account in order to target the right exception level, hence the introduction of a runtime patching callback.
Reviewed-by: Mark Rutland mark.rutland@arm.com Reviewed-by: Julien Grall julien.grall@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 Signed-off-by: Marc Zyngier marc.zyngier@arm.com --- arch/arm64/kernel/cpu_errata.c | 24 ++++++++++++++++++++++++ arch/arm64/kernel/entry.S | 22 ++++++++++++++++++++++ include/linux/arm-smccc.h | 5 +++++ 3 files changed, 51 insertions(+)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index 2de62aa91303..d4cbdbe1d1eb 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -187,6 +187,30 @@ static int enable_smccc_arch_workaround_1(void *data) } #endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */
+#ifdef CONFIG_ARM64_SSBD +void __init arm64_update_smccc_conduit(struct alt_instr *alt, + __le32 *origptr, __le32 *updptr, + int nr_inst) +{ + u32 insn; + + BUG_ON(nr_inst != 1); + + switch (psci_ops.conduit) { + case PSCI_CONDUIT_HVC: + insn = aarch64_insn_get_hvc_value(); + break; + case PSCI_CONDUIT_SMC: + insn = aarch64_insn_get_smc_value(); + break; + default: + return; + } + + *updptr = cpu_to_le32(insn); +} +#endif /* CONFIG_ARM64_SSBD */ + #define MIDR_RANGE(model, min, max) \ .def_scope = SCOPE_LOCAL_CPU, \ .matches = is_affected_midr_range, \ diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 7fed00b47692..7651e9164943 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -18,6 +18,7 @@ * along with this program. If not, see http://www.gnu.org/licenses/. */
+#include <linux/arm-smccc.h> #include <linux/init.h> #include <linux/linkage.h>
@@ -95,6 +96,18 @@ alternative_else_nop_endif add \dst, \dst, #(\sym - .entry.tramp.text) .endm
+ // This macro corrupts x0-x3. It is the caller's duty + // to save/restore them if required. + .macro apply_ssbd, state +#ifdef CONFIG_ARM64_SSBD + mov w0, #ARM_SMCCC_ARCH_WORKAROUND_2 + mov w1, #\state +alternative_cb arm64_update_smccc_conduit + nop // Patched to SMC/HVC #0 +alternative_cb_end +#endif + .endm + .macro kernel_entry, el, regsize = 64 .if \regsize == 32 mov w0, w0 // zero upper 32 bits of x0 @@ -122,6 +135,13 @@ alternative_else_nop_endif ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug disable_step_tsk x19, x20 // exceptions when scheduling.
+ apply_ssbd 1 + +#ifdef CONFIG_ARM64_SSBD + ldp x0, x1, [sp, #16 * 0] + ldp x2, x3, [sp, #16 * 1] +#endif + mov x29, xzr // fp pointed to user-space .else add x21, sp, #S_FRAME_SIZE @@ -190,6 +210,8 @@ alternative_if ARM64_WORKAROUND_845719 alternative_else_nop_endif #endif 3: + apply_ssbd 0 + .endif msr elr_el1, x21 // set up the return data msr spsr_el1, x22 diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index c89da86de99f..ca1d2cc2cdfa 100644 --- a/include/linux/arm-smccc.h +++ b/include/linux/arm-smccc.h @@ -80,6 +80,11 @@ ARM_SMCCC_SMC_32, \ 0, 0x8000)
+#define ARM_SMCCC_ARCH_WORKAROUND_2 \ + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ + ARM_SMCCC_SMC_32, \ + 0, 0x7fff) + #ifndef __ASSEMBLY__
#include <linux/linkage.h>