From: Ard Biesheuvel ardb@kernel.org
commit ff7a167961d1b97e0e205f245f806e564d3505e7 upstream.
With the introduction of PRMT in the ACPI subsystem, the EFI rts workqueue is no longer the only caller of efi_call_virt_pointer() in the kernel. This means the EFI runtime services lock is no longer sufficient to manage concurrent calls into firmware, but also that firmware calls may occur that are not marshalled via the workqueue mechanism, but originate directly from the caller context.
For added robustness, and to ensure that the runtime services have 8 KiB of stack space available as per the EFI spec, introduce a spinlock protected EFI runtime stack of 8 KiB, where the spinlock also ensures serialization between the EFI rts workqueue (which itself serializes EFI runtime calls) and other callers of efi_call_virt_pointer().
While at it, use the stack pivot to avoid reloading the shadow call stack pointer from the ordinary stack, as doing so could produce a gadget to defeat it.
Signed-off-by: Ard Biesheuvel ardb@kernel.org Cc: Lee Jones lee@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/efi.h | 3 +++ arch/arm64/kernel/efi-rt-wrapper.S | 13 ++++++++++++- arch/arm64/kernel/efi.c | 27 +++++++++++++++++++++++++++ 3 files changed, 42 insertions(+), 1 deletion(-)
--- a/arch/arm64/include/asm/efi.h +++ b/arch/arm64/include/asm/efi.h @@ -25,6 +25,7 @@ int efi_set_mapping_permissions(struct m ({ \ efi_virtmap_load(); \ __efi_fpsimd_begin(); \ + spin_lock(&efi_rt_lock); \ })
#define arch_efi_call_virt(p, f, args...) \ @@ -36,10 +37,12 @@ int efi_set_mapping_permissions(struct m
#define arch_efi_call_virt_teardown() \ ({ \ + spin_unlock(&efi_rt_lock); \ __efi_fpsimd_end(); \ efi_virtmap_unload(); \ })
+extern spinlock_t efi_rt_lock; efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...);
#define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT) --- a/arch/arm64/kernel/efi-rt-wrapper.S +++ b/arch/arm64/kernel/efi-rt-wrapper.S @@ -16,6 +16,12 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) */ stp x1, x18, [sp, #16]
+ ldr_l x16, efi_rt_stack_top + mov sp, x16 +#ifdef CONFIG_SHADOW_CALL_STACK + str x18, [sp, #-16]! +#endif + /* * We are lucky enough that no EFI runtime services take more than * 5 arguments, so all are passed in registers rather than via the @@ -29,6 +35,7 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) mov x4, x6 blr x8
+ mov sp, x29 ldp x1, x2, [sp, #16] cmp x2, x18 ldp x29, x30, [sp], #32 @@ -42,6 +49,10 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) * called with preemption disabled and a separate shadow stack is used * for interrupts. */ - mov x18, x2 +#ifdef CONFIG_SHADOW_CALL_STACK + ldr_l x18, efi_rt_stack_top + ldr x18, [x18, #-16] +#endif + b efi_handle_corrupted_x18 // tail call SYM_FUNC_END(__efi_rt_asm_wrapper) --- a/arch/arm64/kernel/efi.c +++ b/arch/arm64/kernel/efi.c @@ -143,3 +143,30 @@ asmlinkage efi_status_t efi_handle_corru pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f); return s; } + +DEFINE_SPINLOCK(efi_rt_lock); + +asmlinkage u64 *efi_rt_stack_top __ro_after_init; + +/* EFI requires 8 KiB of stack space for runtime services */ +static_assert(THREAD_SIZE >= SZ_8K); + +static int __init arm64_efi_rt_init(void) +{ + void *p; + + if (!efi_enabled(EFI_RUNTIME_SERVICES)) + return 0; + + p = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, GFP_KERNEL, + NUMA_NO_NODE, &&l); +l: if (!p) { + pr_warn("Failed to allocate EFI runtime stack\n"); + clear_bit(EFI_RUNTIME_SERVICES, &efi.flags); + return -ENOMEM; + } + + efi_rt_stack_top = p + THREAD_SIZE; + return 0; +} +core_initcall(arm64_efi_rt_init);