xref: /openbmc/linux/arch/x86/coco/tdx/tdcall.S (revision de4c5bac)
1/* SPDX-License-Identifier: GPL-2.0 */
2#include <asm/asm-offsets.h>
3#include <asm/asm.h>
4#include <asm/frame.h>
5#include <asm/unwind_hints.h>
6
7#include <linux/linkage.h>
8#include <linux/bits.h>
9#include <linux/errno.h>
10
11#include "../../virt/vmx/tdx/tdxcall.S"
12
13/*
14 * Bitmasks of exposed registers (with VMM).
15 */
16#define TDX_RDX		BIT(2)
17#define TDX_RBX		BIT(3)
18#define TDX_RSI		BIT(6)
19#define TDX_RDI		BIT(7)
20#define TDX_R8		BIT(8)
21#define TDX_R9		BIT(9)
22#define TDX_R10		BIT(10)
23#define TDX_R11		BIT(11)
24#define TDX_R12		BIT(12)
25#define TDX_R13		BIT(13)
26#define TDX_R14		BIT(14)
27#define TDX_R15		BIT(15)
28
29/*
30 * These registers are clobbered to hold arguments for each
31 * TDVMCALL. They are safe to expose to the VMM.
32 * Each bit in this mask represents a register ID. Bit field
33 * details can be found in TDX GHCI specification, section
34 * titled "TDCALL [TDG.VP.VMCALL] leaf".
35 */
36#define TDVMCALL_EXPOSE_REGS_MASK	\
37	( TDX_RDX | TDX_RBX | TDX_RSI | TDX_RDI | TDX_R8  | TDX_R9  | \
38	  TDX_R10 | TDX_R11 | TDX_R12 | TDX_R13 | TDX_R14 | TDX_R15 )
39
40.section .noinstr.text, "ax"
41
42/*
43 * __tdx_module_call()  - Used by TDX guests to request services from
44 * the TDX module (does not include VMM services) using TDCALL instruction.
45 *
46 * Transforms function call register arguments into the TDCALL register ABI.
47 * After TDCALL operation, TDX module output is saved in @out (if it is
48 * provided by the user).
49 *
50 *-------------------------------------------------------------------------
51 * TDCALL ABI:
52 *-------------------------------------------------------------------------
53 * Input Registers:
54 *
55 * RAX                 - TDCALL Leaf number.
56 * RCX,RDX,R8-R9       - TDCALL Leaf specific input registers.
57 *
58 * Output Registers:
59 *
60 * RAX                 - TDCALL instruction error code.
61 * RCX,RDX,R8-R11      - TDCALL Leaf specific output registers.
62 *
63 *-------------------------------------------------------------------------
64 *
65 * __tdx_module_call() function ABI:
66 *
67 * @fn  (RDI)          - TDCALL Leaf ID,    moved to RAX
68 * @rcx (RSI)          - Input parameter 1, moved to RCX
69 * @rdx (RDX)          - Input parameter 2, moved to RDX
70 * @r8  (RCX)          - Input parameter 3, moved to R8
71 * @r9  (R8)           - Input parameter 4, moved to R9
72 *
73 * @out (R9)           - struct tdx_module_output pointer
74 *                       stored temporarily in R12 (not
75 *                       shared with the TDX module). It
76 *                       can be NULL.
77 *
78 * Return status of TDCALL via RAX.
79 */
80SYM_FUNC_START(__tdx_module_call)
81	FRAME_BEGIN
82	TDX_MODULE_CALL host=0
83	FRAME_END
84	RET
85SYM_FUNC_END(__tdx_module_call)
86
87/*
88 * TDX_HYPERCALL - Make hypercalls to a TDX VMM using TDVMCALL leaf of TDCALL
89 * instruction
90 *
91 * Transforms values in  function call argument struct tdx_hypercall_args @args
92 * into the TDCALL register ABI. After TDCALL operation, VMM output is saved
93 * back in @args, if \ret is 1.
94 *
95 *-------------------------------------------------------------------------
96 * TD VMCALL ABI:
97 *-------------------------------------------------------------------------
98 *
99 * Input Registers:
100 *
101 * RAX                 - TDCALL instruction leaf number (0 - TDG.VP.VMCALL)
102 * RCX                 - BITMAP which controls which part of TD Guest GPR
103 *                       is passed as-is to the VMM and back.
104 * R10                 - Set 0 to indicate TDCALL follows standard TDX ABI
105 *                       specification. Non zero value indicates vendor
106 *                       specific ABI.
107 * R11                 - VMCALL sub function number
108 * RBX, RDX, RDI, RSI  - Used to pass VMCALL sub function specific arguments.
109 * R8-R9, R12-R15      - Same as above.
110 *
111 * Output Registers:
112 *
113 * RAX                 - TDCALL instruction status (Not related to hypercall
114 *                        output).
115 * RBX, RDX, RDI, RSI  - Hypercall sub function specific output values.
116 * R8-R15              - Same as above.
117 *
118 */
119.macro TDX_HYPERCALL ret:req
120	FRAME_BEGIN
121
122	/* Save callee-saved GPRs as mandated by the x86_64 ABI */
123	push %r15
124	push %r14
125	push %r13
126	push %r12
127	push %rbx
128
129	/* Free RDI to be used as TDVMCALL arguments */
130	movq %rdi, %rax
131
132	/* Copy hypercall registers from arg struct: */
133	movq TDX_HYPERCALL_r8(%rax),  %r8
134	movq TDX_HYPERCALL_r9(%rax),  %r9
135	movq TDX_HYPERCALL_r10(%rax), %r10
136	movq TDX_HYPERCALL_r11(%rax), %r11
137	movq TDX_HYPERCALL_r12(%rax), %r12
138	movq TDX_HYPERCALL_r13(%rax), %r13
139	movq TDX_HYPERCALL_r14(%rax), %r14
140	movq TDX_HYPERCALL_r15(%rax), %r15
141	movq TDX_HYPERCALL_rdi(%rax), %rdi
142	movq TDX_HYPERCALL_rsi(%rax), %rsi
143	movq TDX_HYPERCALL_rbx(%rax), %rbx
144	movq TDX_HYPERCALL_rdx(%rax), %rdx
145
146	push %rax
147
148	/* Mangle function call ABI into TDCALL ABI: */
149	/* Set TDCALL leaf ID (TDVMCALL (0)) in RAX */
150	xor %eax, %eax
151
152	movl $TDVMCALL_EXPOSE_REGS_MASK, %ecx
153
154	tdcall
155
156	/*
157	 * RAX!=0 indicates a failure of the TDVMCALL mechanism itself and that
158	 * something has gone horribly wrong with the TDX module.
159	 *
160	 * The return status of the hypercall operation is in a separate
161	 * register (in R10). Hypercall errors are a part of normal operation
162	 * and are handled by callers.
163	 */
164	testq %rax, %rax
165	jne .Lpanic\@
166
167	pop %rax
168
169	.if \ret
170	movq %r8,  TDX_HYPERCALL_r8(%rax)
171	movq %r9,  TDX_HYPERCALL_r9(%rax)
172	movq %r10, TDX_HYPERCALL_r10(%rax)
173	movq %r11, TDX_HYPERCALL_r11(%rax)
174	movq %r12, TDX_HYPERCALL_r12(%rax)
175	movq %r13, TDX_HYPERCALL_r13(%rax)
176	movq %r14, TDX_HYPERCALL_r14(%rax)
177	movq %r15, TDX_HYPERCALL_r15(%rax)
178	movq %rdi, TDX_HYPERCALL_rdi(%rax)
179	movq %rsi, TDX_HYPERCALL_rsi(%rax)
180	movq %rbx, TDX_HYPERCALL_rbx(%rax)
181	movq %rdx, TDX_HYPERCALL_rdx(%rax)
182	.endif
183
184	/* TDVMCALL leaf return code is in R10 */
185	movq %r10, %rax
186
187	/*
188	 * Zero out registers exposed to the VMM to avoid speculative execution
189	 * with VMM-controlled values. This needs to include all registers
190	 * present in TDVMCALL_EXPOSE_REGS_MASK, except RBX, and R12-R15 which
191	 * will be restored.
192	 */
193	xor %r8d,  %r8d
194	xor %r9d,  %r9d
195	xor %r10d, %r10d
196	xor %r11d, %r11d
197	xor %rdi,  %rdi
198	xor %rsi,  %rsi
199	xor %rdx,  %rdx
200
201	/* Restore callee-saved GPRs as mandated by the x86_64 ABI */
202	pop %rbx
203	pop %r12
204	pop %r13
205	pop %r14
206	pop %r15
207
208	FRAME_END
209
210	RET
211.Lpanic\@:
212	call __tdx_hypercall_failed
213	/* __tdx_hypercall_failed never returns */
214	REACHABLE
215	jmp .Lpanic\@
216.endm
217
218/*
219 *
220 * __tdx_hypercall() function ABI:
221 *
222 * @args  (RDI)        - struct tdx_hypercall_args for input
223 *
224 * On successful completion, return the hypercall error code.
225 */
226SYM_FUNC_START(__tdx_hypercall)
227	TDX_HYPERCALL ret=0
228SYM_FUNC_END(__tdx_hypercall)
229
230/*
231 *
232 * __tdx_hypercall_ret() function ABI:
233 *
234 * @args  (RDI)        - struct tdx_hypercall_args for input and output
235 *
236 * On successful completion, return the hypercall error code.
237 */
238SYM_FUNC_START(__tdx_hypercall_ret)
239	TDX_HYPERCALL ret=1
240SYM_FUNC_END(__tdx_hypercall_ret)
241