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SubjectRe: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call
On Tue, Sep 15, 2020 at 02:28:39PM +0300, Jarkko Sakkinen wrote:
> 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..adbd59d41517
> --- /dev/null
> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S

Why not simply

arch/x86/entry/vdso/sgx.S

?

> @@ -0,0 +1,157 @@
> +/* 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"
> +
> +/* Offset of 'struct sgx_enclave_run' relative to %rbp. */
> +#define SGX_ENCLAVE_RUN_PTR 2*8
> +
> +/* Offsets into 'struct sgx_enclave_run'. */
> +#define SGX_ENCLAVE_RUN_TSC 0*8
> +#define SGX_ENCLAVE_RUN_FLAGS 1*8
> +#define SGX_ENCLAVE_RUN_EXIT_REASON 1*8 + 4
> +#define SGX_ENCLAVE_RUN_USER_HANDLER 2*8
> +/* #define SGX_ENCLAVE_RUN_USER_DATA 3*8 */

What's with that guy? Left here as documentation showing what's at 3*8
offset?

> +#define SGX_ENCLAVE_RUN_EXCEPTION 4*8
> +
> +#define SGX_SYNCHRONOUS_EXIT 0
> +#define SGX_EXCEPTION_EXIT 1

Those are in ...uapi/asm/sgx.h too. Unify?

> +
> +/* Offsets into sgx_enter_enclave.exception. */
> +#define SGX_EX_LEAF 0*8
> +#define SGX_EX_TRAPNR 0*8+4
> +#define SGX_EX_ERROR_CODE 0*8+6
> +#define SGX_EX_ADDRESS 1*8
> +
> +.code64
> +.section .text, "ax"
> +
> +SYM_FUNC_START(__vdso_sgx_enter_enclave)
> + /* Prolog */
> + .cfi_startproc

Are the CFI annotations for userspace?

> + 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_input
> + cmp $ERESUME, %eax
> + ja .Linvalid_input
> +
> + mov SGX_ENCLAVE_RUN_PTR(%rbp), %rcx
> +
> + /* No flags are currently defined/supported. */
> + cmpl $0, SGX_ENCLAVE_RUN_FLAGS(%rcx)
> + jne .Linvalid_input
> +
> + /* Load TCS and AEP */

TSC

I can see why you would write "TCS" though - there's a thread control
structure thing too in that patch.

> + mov SGX_ENCLAVE_RUN_TSC(%rcx), %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. */
> + mov SGX_ENCLAVE_RUN_PTR(%rbp), %rbx
> +
> + /* Set exit_reason. */
> + movl $SGX_SYNCHRONOUS_EXIT, SGX_ENCLAVE_RUN_EXIT_REASON(%rbx)
> +
> + /* Invoke userspace's exit handler if one was provided. */
> +.Lhandle_exit:
> + cmpq $0, SGX_ENCLAVE_RUN_USER_HANDLER(%rbx)
> + jne .Linvoke_userspace_handler
> +
> + /* Success, in the sense that ENCLU was attempted. */
> + xor %eax, %eax
> +
> +.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_input:
> + mov $(-EINVAL), %eax
> + jmp .Lout
> +
> +.Lhandle_exception:
> + mov SGX_ENCLAVE_RUN_PTR(%rbp), %rbx
> +
> + /* Set the exit_reason and exception info. */
> + movl $SGX_EXCEPTION_EXIT, SGX_ENCLAVE_RUN_EXIT_REASON(%rbx)
> +
> + mov %eax, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_LEAF)(%rbx)
> + mov %di, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_TRAPNR)(%rbx)
> + mov %si, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_ERROR_CODE)(%rbx)
> + mov %rdx, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_ADDRESS)(%rbx)
> + jmp .Lhandle_exit
> +
> +.Linvoke_userspace_handler:
> + /* Pass the untrusted RSP (at exit) to the callback via %rcx. */
> + mov %rsp, %rcx
> +
> + /* Save @e, %rbx is about to be clobbered. */

I've been wondering what that "@e" thing is and I believe I've found it at the
end: "... @e, the optional sgx_enclave_exception struct"

Yes?

Please rewrite what that "e" is here - I think you wanna say "struct
sgx_enclave_run.exception" instead to clarify.

...

> 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 d0916fb9629e..1564d7f88597 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h

Are all those defines being added to the uapi header, also actually
needed by userspace?

> @@ -72,4 +72,132 @@ struct sgx_enclave_provision {
> __u64 attribute_fd;
> };
>
> +#define SGX_SYNCHRONOUS_EXIT 0
> +#define SGX_EXCEPTION_EXIT 1
> +
> +struct sgx_enclave_run;
> +
> +/**
> + * 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

I'm sure you can avoid that "at the time of enclave exit" repetition.

...

> +/**
> + * typedef vdso_sgx_enter_enclave_t - Prototype for __vdso_sgx_enter_enclave(),
> + * a vDSO function to 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
> + * @r: struct sgx_enclave_run, must be non-NULL
> + *
> + * NOTE: __vdso_sgx_enter_enclave() does not ensure full compliance with the
> + * x86-64 ABI, e.g. doesn't handle XSAVE state. Except for non-volatile
> + * general purpose registers, EFLAGS.DF, and RSP alignment, 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.

That tcs is probably struct sgx_enclave_run.tcs?

> + * 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.

Expand @e and do you mean "@user_handler" with "@handler"?

> + * 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 (ENCLU reached),
> + * -EINVAL if ENCLU leaf is not allowed,
> + * -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,
> + struct sgx_enclave_run *r);
> +
> #endif /* _UAPI_ASM_X86_SGX_H */
> --
> 2.25.1
>

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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