x86/tdx: Do not corrupt frame-pointer in __tdx_hypercall()

If compiled with CONFIG_FRAME_POINTER=y, objtool is not happy that
__tdx_hypercall() messes up RBP:

  objtool: __tdx_hypercall+0x7f: return with modified stack frame

Rework the function to store TDX_HCALL_ flags on stack instead of RBP.

[ dhansen: minor changelog tweaks ]

Fixes: c30c4b2555ba ("x86/tdx: Refactor __tdx_hypercall() to allow pass down more arguments")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/202301290255.buUBs99R-lkp@intel.com
Link: https://lore.kernel.org/all/20230130135354.27674-1-kirill.shutemov%40linux.intel.com

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index 5da06d1a9ba3c8b383ba5e5aff2f59d448323088..2bd436a4790d611ada8d6c3924cfe2420025f9fb 100644 (file)
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -131,11 +131,10 @@ SYM_FUNC_START(__tdx_hypercall)
        push %r13
        push %r12
        push %rbx
-       push %rbp
 
        /* Free RDI and RSI to be used as TDVMCALL arguments */
        movq %rdi, %rax
-       movq %rsi, %rbp
+       push %rsi
 
        /* Copy hypercall registers from arg struct: */
        movq TDX_HYPERCALL_r8(%rax),  %r8
@@ -168,7 +167,7 @@ SYM_FUNC_START(__tdx_hypercall)
         * HLT operation indefinitely. Since this is the not the desired
         * result, conditionally call STI before TDCALL.
         */
-       testq $TDX_HCALL_ISSUE_STI, %rbp
+       testq $TDX_HCALL_ISSUE_STI, 8(%rsp)
        jz .Lskip_sti
        sti
 .Lskip_sti:
@@ -188,7 +187,7 @@ SYM_FUNC_START(__tdx_hypercall)
        pop %rax
 
        /* Copy hypercall result registers to arg struct if needed */
-       testq $TDX_HCALL_HAS_OUTPUT, %rbp
+       testq $TDX_HCALL_HAS_OUTPUT, (%rsp)
        jz .Lout
 
        movq %r8,  TDX_HYPERCALL_r8(%rax)
@@ -218,11 +217,12 @@ SYM_FUNC_START(__tdx_hypercall)
        xor %r10d, %r10d
        xor %r11d, %r11d
        xor %rdi,  %rdi
-       xor %rsi,  %rsi
        xor %rdx,  %rdx
 
+       /* Remove TDX_HCALL_* flags from the stack */
+       pop %rsi
+
        /* Restore callee-saved GPRs as mandated by the x86_64 ABI */
-       pop %rbp
        pop %rbx
        pop %r12
        pop %r13