linux-kernel - [PATCH] x86/tdx: Do not corrupt frame-pointer in __tdx

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Date:   Mon, 30 Jan 2023 16:53:54 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        kernel test robot <lkp@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] x86/tdx: Do not corrupt frame-pointer in __tdx_hypercall()

If compiled with CONFIG_FRAME_POINTER=y, objtool in 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.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: c30c4b2555ba ("x86/tdx: Refactor __tdx_hypercall() to allow pass down more arguments")
Link: https://lore.kernel.org/all/202301290255.buUBs99R-lkp@intel.com
Reported-by: kernel test robot <lkp@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---

The patch is against tip/x86/tdx. tip/sched/core removes
TDX_HCALL_ISSUE_STI. The trird hunk of the patch is not relevant
after that.

---
 arch/x86/coco/tdx/tdcall.S | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index 5da06d1a9ba3..2bd436a4790d 100644
--- 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
-- 
2.39.1