mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
synced 2026-04-18 03:23:53 -04:00
36d83c249e
When neither sysenter32 nor syscall32 is available (on either FRED-capable 64-bit hardware or old 32-bit hardware), there is no reason to do a bunch of stack shuffling in __kernel_vsyscall. Unfortunately, just overwriting the initial "push" instructions will mess up the CFI annotations, so suffer the 3-byte NOP if not applicable. Similarly, inline the int $0x80 when doing inline system calls in the vdso instead of calling __kernel_vsyscall. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://patch.msgid.link/20251216212606.1325678-11-hpa@zytor.com
92 lines
2.7 KiB
ArmAsm
92 lines
2.7 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* AT_SYSINFO entry point
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*/
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#include <linux/linkage.h>
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#include <asm/dwarf2.h>
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#include <asm/cpufeatures.h>
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#include <asm/alternative.h>
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.text
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.globl __kernel_vsyscall
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.type __kernel_vsyscall,@function
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ALIGN
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__kernel_vsyscall:
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CFI_STARTPROC
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/*
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* If using int $0x80, there is no reason to muck about with the
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* stack here. Unfortunately just overwriting the push instructions
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* would mess up the CFI annotations, but it is only a 3-byte
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* NOP in that case. This could be avoided by patching the
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* vdso symbol table (not the code) and entry point, but that
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* would a fair bit of tooling work or by simply compiling
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* two different vDSO images, but that doesn't seem worth it.
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*/
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ALTERNATIVE "int $0x80; ret", "", X86_FEATURE_SYSFAST32
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/*
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* Reshuffle regs so that all of any of the entry instructions
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* will preserve enough state.
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*
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* A really nice entry sequence would be:
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* pushl %edx
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* pushl %ecx
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* movl %esp, %ecx
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*
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* Unfortunately, naughty Android versions between July and December
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* 2015 actually hardcode the traditional Linux SYSENTER entry
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* sequence. That is severely broken for a number of reasons (ask
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* anyone with an AMD CPU, for example). Nonetheless, we try to keep
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* it working approximately as well as it ever worked.
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*
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* This link may elucidate some of the history:
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* https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7
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* personally, I find it hard to understand what's going on there.
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*
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* Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE.
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* Execute an indirect call to the address in the AT_SYSINFO auxv
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* entry. That is the ONLY correct way to make a fast 32-bit system
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* call on Linux. (Open-coding int $0x80 is also fine, but it's
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* slow.)
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*/
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pushl %ecx
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CFI_ADJUST_CFA_OFFSET 4
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CFI_REL_OFFSET ecx, 0
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pushl %edx
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CFI_ADJUST_CFA_OFFSET 4
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CFI_REL_OFFSET edx, 0
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pushl %ebp
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CFI_ADJUST_CFA_OFFSET 4
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CFI_REL_OFFSET ebp, 0
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#define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter"
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#define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall"
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ALTERNATIVE SYSENTER_SEQUENCE, SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
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/* Re-enter using int $0x80 */
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int $0x80
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SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)
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/*
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* Restore EDX and ECX in case they were clobbered. EBP is not
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* clobbered (the kernel restores it), but it's cleaner and
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* probably faster to pop it than to adjust ESP using addl.
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*/
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popl %ebp
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CFI_RESTORE ebp
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CFI_ADJUST_CFA_OFFSET -4
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popl %edx
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CFI_RESTORE edx
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CFI_ADJUST_CFA_OFFSET -4
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popl %ecx
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CFI_RESTORE ecx
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CFI_ADJUST_CFA_OFFSET -4
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RET
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CFI_ENDPROC
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.size __kernel_vsyscall,.-__kernel_vsyscall
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.previous
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