In a past revision of this patch, I had requested a void *misc parameter that could be passed through vdso_sgx_enter_enclave_t into sgx_enclave_exit_handler_t. This request encountered some push back and I dropped the issue. However, I'd like to revisit it or something similar. One way to create a generic interface to SGX is to pass a structure that captures the relevant CPU state from the handler so that it can be evaluated in C code before reentry. Precedent for this approach can be found in struct kvm_run[0]. Currently, however, there is no way to pass a pointer to such a structure directly into the handler. This can be done implicitly by wrapping the struct sgx_enclave_exception in another structure and then using techniques like container_of() to find another field. However, this is made more difficult by the fact that the sgx_enclave_exit_handler_t is not really using the x86_64 sysv calling convention. Therefore, the sgx_enclave_exit_handler_t MUST be written in assembly. This also implies that we can't use techniques like container_of() and must calculate all the offsets manually, which is tedious, error prone and fragile. This is further complicated by the fact that I'm using Rust (as are a number of other consumers), which has no native offsetof support (yes, there is a crate for it, but it requires a number of complex strategies to defeat the compiler which aren't great) and therefore no container_of() support. We could design a standard struct for this (similar to struct kvm_run). But in order to keep performance in check we'd have to define a limited ABI surface (to avoid things like xsave) which wouldn't have the full flexibility of the current approach. This would allow for a kernel provided vDSO function with a normal calling convention, however (which does have some non-trivial value). I think this is a trade-off we should consider (perhaps making it optional?). But at the least, allowing a pass-through void *misc would reduce the complexity of the assembly calculations. [0]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/kvm.h#L263 On Thu, Jul 16, 2020 at 9:58 AM Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote: > > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > An SGX runtime must be aware of the exceptions, which happen inside an > enclave. Introduce a vDSO call that wraps EENTER/ERESUME cycle and returns > the CPU exception back to the caller exactly when it happens. > > Kernel fixups the exception information to RDI, RSI and RDX. The SGX call > vDSO handler fills this information to the user provided buffer or > alternatively trigger user provided callback at the time of the exception. > > The calling convention is custom and does not follow System V x86-64 ABI. > > Suggested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > Acked-by: Jethro Beekman <jethro@xxxxxxxxxxxx> > Tested-by: Jethro Beekman <jethro@xxxxxxxxxxxx> > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > Co-developed-by: Cedric Xing <cedric.xing@xxxxxxxxx> > Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> > --- > arch/x86/entry/vdso/Makefile | 2 + > arch/x86/entry/vdso/vdso.lds.S | 1 + > arch/x86/entry/vdso/vsgx_enter_enclave.S | 131 +++++++++++++++++++++++ > arch/x86/include/asm/enclu.h | 8 ++ > arch/x86/include/uapi/asm/sgx.h | 98 +++++++++++++++++ > 5 files changed, 240 insertions(+) > create mode 100644 arch/x86/entry/vdso/vsgx_enter_enclave.S > create mode 100644 arch/x86/include/asm/enclu.h > > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile > index ebe82b7aecda..f71ad5ebd0c4 100644 > --- a/arch/x86/entry/vdso/Makefile > +++ b/arch/x86/entry/vdso/Makefile > @@ -29,6 +29,7 @@ VDSO32-$(CONFIG_IA32_EMULATION) := y > vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o > vobjs32-y := vdso32/note.o vdso32/system_call.o vdso32/sigreturn.o > vobjs32-y += vdso32/vclock_gettime.o > +vobjs-$(VDSO64-y) += vsgx_enter_enclave.o > > # files to link into kernel > obj-y += vma.o extable.o > @@ -100,6 +101,7 @@ $(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS > CFLAGS_REMOVE_vclock_gettime.o = -pg > CFLAGS_REMOVE_vdso32/vclock_gettime.o = -pg > CFLAGS_REMOVE_vgetcpu.o = -pg > +CFLAGS_REMOVE_vsgx_enter_enclave.o = -pg > > # > # X32 processes use x32 vDSO to access 64bit kernel data. > diff --git a/arch/x86/entry/vdso/vdso.lds.S b/arch/x86/entry/vdso/vdso.lds.S > index 36b644e16272..4bf48462fca7 100644 > --- a/arch/x86/entry/vdso/vdso.lds.S > +++ b/arch/x86/entry/vdso/vdso.lds.S > @@ -27,6 +27,7 @@ VERSION { > __vdso_time; > clock_getres; > __vdso_clock_getres; > + __vdso_sgx_enter_enclave; > local: *; > }; > } > diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S > new file mode 100644 > index 000000000000..be7e467e1efb > --- /dev/null > +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S > @@ -0,0 +1,131 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +#include <linux/linkage.h> > +#include <asm/export.h> > +#include <asm/errno.h> > +#include <asm/enclu.h> > + > +#include "extable.h" > + > +#define EX_LEAF 0*8 > +#define EX_TRAPNR 0*8+4 > +#define EX_ERROR_CODE 0*8+6 > +#define EX_ADDRESS 1*8 > + > +.code64 > +.section .text, "ax" > + > +SYM_FUNC_START(__vdso_sgx_enter_enclave) > + /* Prolog */ > + .cfi_startproc > + push %rbp > + .cfi_adjust_cfa_offset 8 > + .cfi_rel_offset %rbp, 0 > + mov %rsp, %rbp > + .cfi_def_cfa_register %rbp > + push %rbx > + .cfi_rel_offset %rbx, -8 > + > + mov %ecx, %eax > +.Lenter_enclave: > + /* EENTER <= leaf <= ERESUME */ > + cmp $EENTER, %eax > + jb .Linvalid_leaf > + cmp $ERESUME, %eax > + ja .Linvalid_leaf > + > + /* Load TCS and AEP */ > + mov 0x10(%rbp), %rbx > + lea .Lasync_exit_pointer(%rip), %rcx > + > + /* Single ENCLU serving as both EENTER and AEP (ERESUME) */ > +.Lasync_exit_pointer: > +.Lenclu_eenter_eresume: > + enclu > + > + /* EEXIT jumps here unless the enclave is doing something fancy. */ > + xor %eax, %eax > + > + /* Invoke userspace's exit handler if one was provided. */ > +.Lhandle_exit: > + cmp $0, 0x20(%rbp) > + jne .Linvoke_userspace_handler > + > +.Lout: > + pop %rbx > + leave > + .cfi_def_cfa %rsp, 8 > + ret > + > + /* The out-of-line code runs with the pre-leave stack frame. */ > + .cfi_def_cfa %rbp, 16 > + > +.Linvalid_leaf: > + mov $(-EINVAL), %eax > + jmp .Lout > + > +.Lhandle_exception: > + mov 0x18(%rbp), %rcx > + test %rcx, %rcx > + je .Lskip_exception_info > + > + /* Fill optional exception info. */ > + mov %eax, EX_LEAF(%rcx) > + mov %di, EX_TRAPNR(%rcx) > + mov %si, EX_ERROR_CODE(%rcx) > + mov %rdx, EX_ADDRESS(%rcx) > +.Lskip_exception_info: > + mov $(-EFAULT), %eax > + jmp .Lhandle_exit > + > +.Linvoke_userspace_handler: > + /* Pass the untrusted RSP (at exit) to the callback via %rcx. */ > + mov %rsp, %rcx > + > + /* Save the untrusted RSP offset in %rbx (non-volatile register). */ > + mov %rsp, %rbx > + and $0xf, %rbx > + > + /* > + * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned > + * _after_ pushing the parameters on the stack, hence the bonus push. > + */ > + and $-0x10, %rsp > + push %rax > + > + /* Push @e, the "return" value and @tcs as params to the callback. */ > + push 0x18(%rbp) > + push %rax > + push 0x10(%rbp) > + > + /* Clear RFLAGS.DF per x86_64 ABI */ > + cld > + > + /* Load the callback pointer to %rax and invoke it via retpoline. */ > + mov 0x20(%rbp), %rax > + call .Lretpoline > + > + /* Undo the post-exit %rsp adjustment. */ > + lea 0x20(%rsp, %rbx), %rsp > + > + /* > + * If the return from callback is zero or negative, return immediately, > + * else re-execute ENCLU with the postive return value interpreted as > + * the requested ENCLU leaf. > + */ > + cmp $0, %eax > + jle .Lout > + jmp .Lenter_enclave > + > +.Lretpoline: > + call 2f > +1: pause > + lfence > + jmp 1b > +2: mov %rax, (%rsp) > + ret > + .cfi_endproc > + > +_ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception) > + > +SYM_FUNC_END(__vdso_sgx_enter_enclave) > diff --git a/arch/x86/include/asm/enclu.h b/arch/x86/include/asm/enclu.h > new file mode 100644 > index 000000000000..06157b3e9ede > --- /dev/null > +++ b/arch/x86/include/asm/enclu.h > @@ -0,0 +1,8 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _ASM_X86_ENCLU_H > +#define _ASM_X86_ENCLU_H > + > +#define EENTER 0x02 > +#define ERESUME 0x03 > + > +#endif /* _ASM_X86_ENCLU_H */ > diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h > index 57d0d30c79b3..3760e5d5dc0c 100644 > --- a/arch/x86/include/uapi/asm/sgx.h > +++ b/arch/x86/include/uapi/asm/sgx.h > @@ -74,4 +74,102 @@ struct sgx_enclave_set_attribute { > __u64 attribute_fd; > }; > > +/** > + * struct sgx_enclave_exception - structure to report exceptions encountered in > + * __vdso_sgx_enter_enclave() > + * > + * @leaf: ENCLU leaf from \%eax at time of exception > + * @trapnr: exception trap number, a.k.a. fault vector > + * @error_code: exception error code > + * @address: exception address, e.g. CR2 on a #PF > + * @reserved: reserved for future use > + */ > +struct sgx_enclave_exception { > + __u32 leaf; > + __u16 trapnr; > + __u16 error_code; > + __u64 address; > + __u64 reserved[2]; > +}; > + > +/** > + * typedef sgx_enclave_exit_handler_t - Exit handler function accepted by > + * __vdso_sgx_enter_enclave() > + * > + * @rdi: RDI at the time of enclave exit > + * @rsi: RSI at the time of enclave exit > + * @rdx: RDX at the time of enclave exit > + * @ursp: RSP at the time of enclave exit (untrusted stack) > + * @r8: R8 at the time of enclave exit > + * @r9: R9 at the time of enclave exit > + * @tcs: Thread Control Structure used to enter enclave > + * @ret: 0 on success (EEXIT), -EFAULT on an exception > + * @e: Pointer to struct sgx_enclave_exception (as provided by caller) > + */ > +typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, > + long ursp, long r8, long r9, > + void *tcs, int ret, > + struct sgx_enclave_exception *e); > + > +/** > + * __vdso_sgx_enter_enclave() - Enter an SGX enclave > + * @rdi: Pass-through value for RDI > + * @rsi: Pass-through value for RSI > + * @rdx: Pass-through value for RDX > + * @leaf: ENCLU leaf, must be EENTER or ERESUME > + * @r8: Pass-through value for R8 > + * @r9: Pass-through value for R9 > + * @tcs: TCS, must be non-NULL > + * @e: Optional struct sgx_enclave_exception instance > + * @handler: Optional enclave exit handler > + * > + * NOTE: __vdso_sgx_enter_enclave() does not ensure full compliance with the > + * x86-64 ABI, e.g. doesn't explicitly clear EFLAGS.DF after EEXIT. Except for > + * non-volatile general purpose registers, preserving/setting state in > + * accordance with the x86-64 ABI is the responsibility of the enclave and its > + * runtime, i.e. __vdso_sgx_enter_enclave() cannot be called from C code > + * without careful consideration by both the enclave and its runtime. > + * > + * All general purpose registers except RAX, RBX and RCX are passed as-is to > + * the enclave. RAX, RBX and RCX are consumed by EENTER and ERESUME and are > + * loaded with @leaf, asynchronous exit pointer, and @tcs respectively. > + * > + * RBP and the stack are used to anchor __vdso_sgx_enter_enclave() to the > + * pre-enclave state, e.g. to retrieve @e and @handler after an enclave exit. > + * All other registers are available for use by the enclave and its runtime, > + * e.g. an enclave can push additional data onto the stack (and modify RSP) to > + * pass information to the optional exit handler (see below). > + * > + * Most exceptions reported on ENCLU, including those that occur within the > + * enclave, are fixed up and reported synchronously instead of being delivered > + * via a standard signal. Debug Exceptions (#DB) and Breakpoints (#BP) are > + * never fixed up and are always delivered via standard signals. On synchrously > + * reported exceptions, -EFAULT is returned and details about the exception are > + * recorded in @e, the optional sgx_enclave_exception struct. > + > + * If an exit handler is provided, the handler will be invoked on synchronous > + * exits from the enclave and for all synchronously reported exceptions. In > + * latter case, @e is filled prior to invoking the handler. > + * > + * The exit handler's return value is interpreted as follows: > + * >0: continue, restart __vdso_sgx_enter_enclave() with @ret as @leaf > + * 0: success, return @ret to the caller > + * <0: error, return @ret to the caller > + * > + * The exit handler may transfer control, e.g. via longjmp() or C++ exception, > + * without returning to __vdso_sgx_enter_enclave(). > + * > + * Return: > + * 0 on success, > + * -EINVAL if ENCLU leaf is not allowed, > + * -EFAULT if an exception occurs on ENCLU or within the enclave > + * -errno for all other negative values returned by the userspace exit handler > + */ > +typedef int (*vdso_sgx_enter_enclave_t)(unsigned long rdi, unsigned long rsi, > + unsigned long rdx, unsigned int leaf, > + unsigned long r8, unsigned long r9, > + void *tcs, > + struct sgx_enclave_exception *e, > + sgx_enclave_exit_handler_t handler); > + > #endif /* _UAPI_ASM_X86_SGX_H */ > -- > 2.25.1 >
