Messages in this thread Patch in this message | | | From | Lai Jiangshan <> | Subject | [PATCH 25/24] x86/traps: Rewrite native_load_gs_index in C code | Date | Thu, 2 Sep 2021 18:50:51 +0800 |
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From: Lai Jiangshan <laijs@linux.alibaba.com>
There is no constrain/limition to force native_load_gs_index() to be in ASM code.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> --- arch/x86/entry/entry_64.S | 36 ---------------------------- arch/x86/entry/traps.c | 25 +++++++++++++++++++ arch/x86/include/asm/special_insns.h | 11 +-------- arch/x86/mm/extable.c | 15 ++++++++++++ 4 files changed, 41 insertions(+), 46 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 2d17fca1f503..16ee481e9b5f 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -659,42 +659,6 @@ native_irq_return_ldt: SYM_CODE_END(common_interrupt_return) _ASM_NOKPROBE(common_interrupt_return) -/* - * Reload gs selector with exception handling - * edi: new selector - * - * Is in entry.text as it shouldn't be instrumented. - */ -SYM_FUNC_START(asm_load_gs_index) - FRAME_BEGIN - swapgs -SYM_INNER_LABEL(asm_load_gs_index_gs_change, SYM_L_GLOBAL) -.Lgs_change: - movl %edi, %gs -2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE - swapgs - FRAME_END - ret -SYM_FUNC_END(asm_load_gs_index) -EXPORT_SYMBOL(asm_load_gs_index) - - _ASM_EXTABLE(.Lgs_change, .Lbad_gs) - .section .fixup, "ax" - /* running with kernelgs */ -SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs) - swapgs /* switch back to user gs */ -.macro ZAP_GS - /* This can't be a string because the preprocessor needs to see it. */ - movl $__USER_DS, %eax - movl %eax, %gs -.endm - ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG - xorl %eax, %eax - movl %eax, %gs - jmp 2b -SYM_CODE_END(.Lbad_gs) - .previous - #ifdef CONFIG_XEN_PV /* * A note on the "critical region" in our callback handler. diff --git a/arch/x86/entry/traps.c b/arch/x86/entry/traps.c index 52511db6baa6..2a17d74569fd 100644 --- a/arch/x86/entry/traps.c +++ b/arch/x86/entry/traps.c @@ -679,6 +679,31 @@ DEFINE_IDTENTRY_RAW(exc_int3) } #ifdef CONFIG_X86_64 + +/* + * Reload gs selector with exception handling + * selector: new selector + * + * Is noinstr as it shouldn't be instrumented. + */ +noinstr void native_load_gs_index(unsigned int selector) +{ + unsigned long flags; + + local_irq_save(flags); + native_swapgs(); + asm volatile( + ".global asm_load_gs_index_gs_change \n" + "asm_load_gs_index_gs_change: \n" + "1: movl %0, %%gs \n" + " swapgs \n" + "2: \n" + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_clear_gs) + :: "r" (selector) : "memory"); + alternative("", "mfence", X86_BUG_SWAPGS_FENCE); + local_irq_restore(flags); +} + /* * Help handler running on a per-cpu (IST or entry trampoline) stack * to switch to the normal thread stack if the interrupted code was in diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 058995bb153c..c5d74ebce527 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -120,16 +120,7 @@ static inline void native_wbinvd(void) asm volatile("wbinvd": : :"memory"); } -extern asmlinkage void asm_load_gs_index(unsigned int selector); - -static inline void native_load_gs_index(unsigned int selector) -{ - unsigned long flags; - - local_irq_save(flags); - asm_load_gs_index(selector); - local_irq_restore(flags); -} +extern asmlinkage void native_load_gs_index(unsigned int selector); static inline unsigned long __read_cr4(void) { diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index e1664e9f969c..695a580a652a 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -138,6 +138,21 @@ __visible bool ex_handler_clear_fs(const struct exception_table_entry *fixup, } EXPORT_SYMBOL(ex_handler_clear_fs); +__visible bool ex_handler_clear_gs(const struct exception_table_entry *fixup, + struct pt_regs *regs, int trapnr, + unsigned long error_code, + unsigned long fault_addr) +{ + /* + * The following native_load_gs_index() should not fault, otherwise + * it would be infinite recursion. + */ + if (static_cpu_has(X86_BUG_NULL_SEG)) + native_load_gs_index(__USER_DS); + native_load_gs_index(0); + return ex_handler_default(fixup, regs, trapnr, error_code, fault_addr); +} + enum handler_type ex_get_fault_handler_type(unsigned long ip) { const struct exception_table_entry *e; -- 2.19.1.6.gb485710b
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