From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit e8dfdf3162eb549d064b8c10b1564f7e8ee82591 ]
Unlike x86, which has machinery to deal with page faults that occur during the execution of EFI runtime services, arm64 has nothing like that, and a synchronous exception raised by firmware code brings down the whole system.
With more EFI based systems appearing that were not built to run Linux (such as the Windows-on-ARM laptops based on Qualcomm SOCs), as well as the introduction of PRM (platform specific firmware routines that are callable just like EFI runtime services), we are more likely to run into issues of this sort, and it is much more likely that we can identify and work around such issues if they don't bring down the system entirely.
Since we already use a EFI runtime services call wrapper in assembler, we can quite easily add some code that captures the execution state at the point where the call is made, allowing us to revert to this state and proceed execution if the call triggered a synchronous exception.
Given that the kernel and the firmware don't share any data structures that could end up in an indeterminate state, we can happily continue running, as long as we mark the EFI runtime services as unavailable from that point on.
Signed-off-by: Ard Biesheuvel ardb@kernel.org Acked-by: Catalin Marinas catalin.marinas@arm.com Stable-dep-of: 8a9a1a18731e ("arm64: efi: Avoid workqueue to check whether EFI runtime is live") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/include/asm/efi.h | 8 +++++++ arch/arm64/kernel/efi-rt-wrapper.S | 32 +++++++++++++++++++++---- arch/arm64/kernel/efi.c | 22 +++++++++++++++++ arch/arm64/mm/fault.c | 4 ++++ drivers/firmware/efi/runtime-wrappers.c | 1 + 5 files changed, 62 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h index b9f3165075c9..0edaf8e385b8 100644 --- a/arch/arm64/include/asm/efi.h +++ b/arch/arm64/include/asm/efi.h @@ -14,8 +14,16 @@
#ifdef CONFIG_EFI extern void efi_init(void); + +bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg); #else #define efi_init() + +static inline +bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg) +{ + return false; +} #endif
int efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md); diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S index 2d3c4b02393e..d872d18101d8 100644 --- a/arch/arm64/kernel/efi-rt-wrapper.S +++ b/arch/arm64/kernel/efi-rt-wrapper.S @@ -7,7 +7,7 @@ #include <asm/assembler.h>
SYM_FUNC_START(__efi_rt_asm_wrapper) - stp x29, x30, [sp, #-32]! + stp x29, x30, [sp, #-112]! mov x29, sp
/* @@ -17,11 +17,21 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) */ stp x1, x18, [sp, #16]
+ /* + * Preserve all callee saved registers and preserve the stack pointer + * value at the base of the EFI runtime stack so we can recover from + * synchronous exceptions occurring while executing the firmware + * routines. + */ + stp x19, x20, [sp, #32] + stp x21, x22, [sp, #48] + stp x23, x24, [sp, #64] + stp x25, x26, [sp, #80] + stp x27, x28, [sp, #96] + ldr_l x16, efi_rt_stack_top mov sp, x16 -#ifdef CONFIG_SHADOW_CALL_STACK - str x18, [sp, #-16]! -#endif + stp x18, x29, [sp, #-16]!
/* * We are lucky enough that no EFI runtime services take more than @@ -39,7 +49,7 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) mov sp, x29 ldp x1, x2, [sp, #16] cmp x2, x18 - ldp x29, x30, [sp], #32 + ldp x29, x30, [sp], #112 b.ne 0f ret 0: @@ -57,3 +67,15 @@ SYM_FUNC_START(__efi_rt_asm_wrapper)
b efi_handle_corrupted_x18 // tail call SYM_FUNC_END(__efi_rt_asm_wrapper) + +SYM_CODE_START(__efi_rt_asm_recover) + mov sp, x30 + + ldp x19, x20, [sp, #32] + ldp x21, x22, [sp, #48] + ldp x23, x24, [sp, #64] + ldp x25, x26, [sp, #80] + ldp x27, x28, [sp, #96] + ldp x29, x30, [sp], #112 + ret +SYM_CODE_END(__efi_rt_asm_recover) diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c index 386bd81ca12b..fab05de2e12d 100644 --- a/arch/arm64/kernel/efi.c +++ b/arch/arm64/kernel/efi.c @@ -149,6 +149,28 @@ DEFINE_SPINLOCK(efi_rt_lock);
asmlinkage u64 *efi_rt_stack_top __ro_after_init;
+asmlinkage efi_status_t __efi_rt_asm_recover(void); + +bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg) +{ + /* Check whether the exception occurred while running the firmware */ + if (current_work() != &efi_rts_work.work || regs->pc >= TASK_SIZE_64) + return false; + + pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg); + add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK); + clear_bit(EFI_RUNTIME_SERVICES, &efi.flags); + + regs->regs[0] = EFI_ABORTED; + regs->regs[30] = efi_rt_stack_top[-1]; + regs->pc = (u64)__efi_rt_asm_recover; + + if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) + regs->regs[18] = efi_rt_stack_top[-2]; + + return true; +} + /* EFI requires 8 KiB of stack space for runtime services */ static_assert(THREAD_SIZE >= SZ_8K);
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 74f76514a48d..3eb2825d08cf 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -30,6 +30,7 @@ #include <asm/bug.h> #include <asm/cmpxchg.h> #include <asm/cpufeature.h> +#include <asm/efi.h> #include <asm/exception.h> #include <asm/daifflags.h> #include <asm/debug-monitors.h> @@ -397,6 +398,9 @@ static void __do_kernel_fault(unsigned long addr, unsigned long esr, msg = "paging request"; }
+ if (efi_runtime_fixup_exception(regs, msg)) + return; + die_kernel_fault(msg, addr, esr, regs); }
diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c index 60075e0e4943..1fba4e09cdcf 100644 --- a/drivers/firmware/efi/runtime-wrappers.c +++ b/drivers/firmware/efi/runtime-wrappers.c @@ -84,6 +84,7 @@ struct efi_runtime_work efi_rts_work; else \ pr_err("Failed to queue work to efi_rts_wq.\n"); \ \ + WARN_ON_ONCE(efi_rts_work.status == EFI_ABORTED); \ exit: \ efi_rts_work.efi_rts_id = EFI_NONE; \ efi_rts_work.status; \