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/*
* Copyright (c) 2017-2022, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <stdbool.h>
#include <string.h>
#include <arch_helpers.h>
#include <context.h>
#include <lib/el3_runtime/context_mgmt.h>
#include <lib/psci/psci.h>
#include <lib/utils.h>
#include <plat/arm/common/plat_arm.h>
#include <smccc_helpers.h>
/*
* Handle SMC from a lower exception level to switch its execution state
* (either from AArch64 to AArch32, or vice versa).
*
* smc_fid:
* SMC function ID - either ARM_SIP_SVC_STATE_SWITCH_64 or
* ARM_SIP_SVC_STATE_SWITCH_32.
* pc_hi, pc_lo:
* PC upon re-entry to the calling exception level; width dependent on the
* calling exception level.
* cookie_hi, cookie_lo:
* Opaque pointer pairs received from the caller to pass it back, upon
* re-entry.
* handle:
* Handle to saved context.
*/
int arm_execution_state_switch(unsigned int smc_fid,
uint32_t pc_hi,
uint32_t pc_lo,
uint32_t cookie_hi,
uint32_t cookie_lo,
void *handle)
{
bool caller_64, thumb = false, from_el2;
unsigned int el, endianness;
u_register_t spsr, pc, scr, sctlr;
entry_point_info_t ep;
cpu_context_t *ctx = (cpu_context_t *) handle;
el3_state_t *el3_ctx = get_el3state_ctx(ctx);
/* Validate supplied entry point */
pc = (u_register_t) (((uint64_t) pc_hi << 32) | pc_lo);
if (arm_validate_ns_entrypoint(pc) != 0)
goto invalid_param;
/* That the SMC originated from NS is already validated by the caller */
/*
* Disallow state switch if any of the secondaries have been brought up.
*/
if (psci_secondaries_brought_up() != 0)
goto exec_denied;
spsr = read_ctx_reg(el3_ctx, CTX_SPSR_EL3);
caller_64 = (GET_RW(spsr) == MODE_RW_64);
if (caller_64) {
/*
* If the call originated from AArch64, expect 32-bit pointers when
* switching to AArch32.
*/
if ((pc_hi != 0U) || (cookie_hi != 0U))
goto invalid_param;
pc = pc_lo;
/* Instruction state when entering AArch32 */
thumb = (pc & 1U) != 0U;
} else {
/* Construct AArch64 PC */
pc = (((u_register_t) pc_hi) << 32) | pc_lo;
}
/* Make sure PC is 4-byte aligned, except for Thumb */
if (((pc & 0x3U) != 0U) && !thumb)
goto invalid_param;
/*
* EL3 controls register width of the immediate lower EL only. Expect
* this request from EL2/Hyp unless:
*
* - EL2 is not implemented;
* - EL2 is implemented, but was disabled. This can be inferred from
* SCR_EL3.HCE.
*/
from_el2 = caller_64 ? (GET_EL(spsr) == MODE_EL2) :
(GET_M32(spsr) == MODE32_hyp);
scr = read_ctx_reg(el3_ctx, CTX_SCR_EL3);
if (!from_el2) {
/* The call is from NS privilege level other than HYP */
/*
* Disallow switching state if there's a Hypervisor in place;
* this request must be taken up with the Hypervisor instead.
*/
if ((scr & SCR_HCE_BIT) != 0U)
goto exec_denied;
}
/*
* Return to the caller using the same endianness. Extract
* endianness bit from the respective system control register
* directly.
*/
sctlr = from_el2 ? read_sctlr_el2() : read_sctlr_el1();
endianness = ((sctlr & SCTLR_EE_BIT) != 0U) ? 1U : 0U;
/* Construct SPSR for the exception state we're about to switch to */
if (caller_64) {
unsigned long long impl;
/*
* Switching from AArch64 to AArch32. Ensure this CPU implements
* the target EL in AArch32.
*/
impl = from_el2 ? el_implemented(2) : el_implemented(1);
if (impl != EL_IMPL_A64_A32)
goto exec_denied;
/* Return to the equivalent AArch32 privilege level */
el = from_el2 ? MODE32_hyp : MODE32_svc;
spsr = SPSR_MODE32((u_register_t) el,
thumb ? SPSR_T_THUMB : SPSR_T_ARM,
endianness, DISABLE_ALL_EXCEPTIONS);
} else {
/*
* Switching from AArch32 to AArch64. Since it's not possible to
* implement an EL as AArch32-only (from which this call was
* raised), it's safe to assume AArch64 is also implemented.
*/
el = from_el2 ? MODE_EL2 : MODE_EL1;
spsr = SPSR_64((u_register_t) el, MODE_SP_ELX,
DISABLE_ALL_EXCEPTIONS);
}
/*
* Use the context management library to re-initialize the existing
* context with the execution state flipped. Since the library takes
* entry_point_info_t pointer as the argument, construct a dummy one
* with PC, state width, endianness, security etc. appropriately set.
* Other entries in the entry point structure are irrelevant for
* purpose.
*/
zeromem(&ep, sizeof(ep));
ep.pc = pc;
ep.spsr = (uint32_t) spsr;
SET_PARAM_HEAD(&ep, PARAM_EP, VERSION_1,
((unsigned int) ((endianness != 0U) ? EP_EE_BIG :
EP_EE_LITTLE)
| NON_SECURE | EP_ST_DISABLE));
/*
* Re-initialize the system register context, and exit EL3 as if for the
* first time. State switch is effectively a soft reset of the
* calling EL.
*/
cm_init_my_context(&ep);
cm_prepare_el3_exit_ns();
/*
* State switch success. The caller of SMC wouldn't see the SMC
* returning. Instead, execution starts at the supplied entry point,
* with context pointers populated in registers 0 and 1.
*/
SMC_RET2(handle, cookie_hi, cookie_lo);
invalid_param:
SMC_RET1(handle, STATE_SW_E_PARAM);
exec_denied:
/* State switch denied */
SMC_RET1(handle, STATE_SW_E_DENIED);
}
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