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Message-Id: <ed167304-0d43-42fb-9da1-1358dded3a2f@www.fastmail.com>
Date: Wed, 20 Apr 2022 07:26:54 -0700
From: "Andy Lutomirski" <luto@...nel.org>
To: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
"the arch/x86 maintainers" <x86@...nel.org>,
"Josh Poimboeuf" <jpoimboe@...hat.com>,
"Brian Gerst" <brgerst@...il.com>,
"Lai Jiangshan" <jiangshanlai@...il.com>,
"Andrew Cooper" <Andrew.Cooper3@...rix.com>
Cc: "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86,entry: Use PUSH_AND_CLEAR_REGS for compat
On Tue, Apr 19, 2022, at 1:41 PM, Peter Zijlstra wrote:
> Since the upper regs don't exist for ia32 code, preserving them
> doesn't hurt and it simplifies the code.
They exist for compat code, though, and should be preserved for ABI purposes. Programs that do int $0x80 in 64-bit code do exist.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> arch/x86/entry/calling.h | 9 ++--
> arch/x86/entry/entry_64_compat.S | 87 +--------------------------------------
> 2 files changed, 8 insertions(+), 88 deletions(-)
>
> --- a/arch/x86/entry/calling.h
> +++ b/arch/x86/entry/calling.h
> @@ -63,13 +63,15 @@ For 32-bit we have the following convent
> * for assembly code:
> */
>
> -.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0
> +.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0 save_rdi=1
> .if \save_ret
> pushq %rsi /* pt_regs->si */
> movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */
> movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */
> .else
> + .if \save_rdi
> pushq %rdi /* pt_regs->di */
> + .endif
> pushq %rsi /* pt_regs->si */
> .endif
> pushq \rdx /* pt_regs->dx */
> @@ -111,11 +113,10 @@ For 32-bit we have the following convent
> xorl %r13d, %r13d /* nospec r13 */
> xorl %r14d, %r14d /* nospec r14 */
> xorl %r15d, %r15d /* nospec r15 */
> -
> .endm
>
> -.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
> - PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret
> +.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0 save_rdi=1
> + PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret save_rdi=\save_rdi
> CLEAR_REGS
> .endm
>
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -83,32 +83,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_af
> movl %eax, %eax
>
> pushq %rax /* pt_regs->orig_ax */
> - pushq %rdi /* pt_regs->di */
> - pushq %rsi /* pt_regs->si */
> - pushq %rdx /* pt_regs->dx */
> - pushq %rcx /* pt_regs->cx */
> - pushq $-ENOSYS /* pt_regs->ax */
> - pushq $0 /* pt_regs->r8 = 0 */
> - xorl %r8d, %r8d /* nospec r8 */
> - pushq $0 /* pt_regs->r9 = 0 */
> - xorl %r9d, %r9d /* nospec r9 */
> - pushq $0 /* pt_regs->r10 = 0 */
> - xorl %r10d, %r10d /* nospec r10 */
> - pushq $0 /* pt_regs->r11 = 0 */
> - xorl %r11d, %r11d /* nospec r11 */
> - pushq %rbx /* pt_regs->rbx */
> - xorl %ebx, %ebx /* nospec rbx */
> - pushq %rbp /* pt_regs->rbp (will be overwritten) */
> - xorl %ebp, %ebp /* nospec rbp */
> - pushq $0 /* pt_regs->r12 = 0 */
> - xorl %r12d, %r12d /* nospec r12 */
> - pushq $0 /* pt_regs->r13 = 0 */
> - xorl %r13d, %r13d /* nospec r13 */
> - pushq $0 /* pt_regs->r14 = 0 */
> - xorl %r14d, %r14d /* nospec r14 */
> - pushq $0 /* pt_regs->r15 = 0 */
> - xorl %r15d, %r15d /* nospec r15 */
> -
> + PUSH_AND_CLEAR_REGS rax=$-ENOSYS
> UNWIND_HINT_REGS
>
> cld
> @@ -225,35 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_saf
> SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
> movl %eax, %eax /* discard orig_ax high bits */
> pushq %rax /* pt_regs->orig_ax */
> - pushq %rdi /* pt_regs->di */
> - pushq %rsi /* pt_regs->si */
> - xorl %esi, %esi /* nospec si */
> - pushq %rdx /* pt_regs->dx */
> - xorl %edx, %edx /* nospec dx */
> - pushq %rbp /* pt_regs->cx (stashed in bp) */
> - xorl %ecx, %ecx /* nospec cx */
> - pushq $-ENOSYS /* pt_regs->ax */
> - pushq $0 /* pt_regs->r8 = 0 */
> - xorl %r8d, %r8d /* nospec r8 */
> - pushq $0 /* pt_regs->r9 = 0 */
> - xorl %r9d, %r9d /* nospec r9 */
> - pushq $0 /* pt_regs->r10 = 0 */
> - xorl %r10d, %r10d /* nospec r10 */
> - pushq $0 /* pt_regs->r11 = 0 */
> - xorl %r11d, %r11d /* nospec r11 */
> - pushq %rbx /* pt_regs->rbx */
> - xorl %ebx, %ebx /* nospec rbx */
> - pushq %rbp /* pt_regs->rbp (will be overwritten) */
> - xorl %ebp, %ebp /* nospec rbp */
> - pushq $0 /* pt_regs->r12 = 0 */
> - xorl %r12d, %r12d /* nospec r12 */
> - pushq $0 /* pt_regs->r13 = 0 */
> - xorl %r13d, %r13d /* nospec r13 */
> - pushq $0 /* pt_regs->r14 = 0 */
> - xorl %r14d, %r14d /* nospec r14 */
> - pushq $0 /* pt_regs->r15 = 0 */
> - xorl %r15d, %r15d /* nospec r15 */
> -
> + PUSH_AND_CLEAR_REGS rax=$-ENOSYS
> UNWIND_HINT_REGS
>
> movq %rsp, %rdi
> @@ -381,35 +328,7 @@ SYM_CODE_START(entry_INT80_compat)
> pushq 1*8(%rdi) /* regs->orig_ax */
> pushq (%rdi) /* pt_regs->di */
> .Lint80_keep_stack:
> -
> - pushq %rsi /* pt_regs->si */
> - xorl %esi, %esi /* nospec si */
> - pushq %rdx /* pt_regs->dx */
> - xorl %edx, %edx /* nospec dx */
> - pushq %rcx /* pt_regs->cx */
> - xorl %ecx, %ecx /* nospec cx */
> - pushq $-ENOSYS /* pt_regs->ax */
> - pushq %r8 /* pt_regs->r8 */
> - xorl %r8d, %r8d /* nospec r8 */
> - pushq %r9 /* pt_regs->r9 */
> - xorl %r9d, %r9d /* nospec r9 */
> - pushq %r10 /* pt_regs->r10*/
> - xorl %r10d, %r10d /* nospec r10 */
> - pushq %r11 /* pt_regs->r11 */
> - xorl %r11d, %r11d /* nospec r11 */
> - pushq %rbx /* pt_regs->rbx */
> - xorl %ebx, %ebx /* nospec rbx */
> - pushq %rbp /* pt_regs->rbp */
> - xorl %ebp, %ebp /* nospec rbp */
> - pushq %r12 /* pt_regs->r12 */
> - xorl %r12d, %r12d /* nospec r12 */
> - pushq %r13 /* pt_regs->r13 */
> - xorl %r13d, %r13d /* nospec r13 */
> - pushq %r14 /* pt_regs->r14 */
> - xorl %r14d, %r14d /* nospec r14 */
> - pushq %r15 /* pt_regs->r15 */
> - xorl %r15d, %r15d /* nospec r15 */
> -
> + PUSH_AND_CLEAR_REGS save_rdi=0
> UNWIND_HINT_REGS
>
> cld
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