Messages in this thread Patch in this message | | | From | Lai Jiangshan <> | Subject | [PATCH V3 7/7] x86/entry: Implement the whole error_entry() as C code | Date | Mon, 6 Jun 2022 22:45:09 +0800 |
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From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Implement error_entry() as C code in arch/x86/entry/entry64.c and replace the ASM version of error_entry().
The code might be in the user CR3 and user GS base at the start of the function so it calls __always_inline C function only until the GS and CR3 is switched.
No functional change intended and comments are also copied.
The C version generally has better readability and easier to be updated/improved.
Note: To avoid using goto, the C code has two call sites of sync_regs(). It calls sync_regs() directly after fixup_bad_iret() returns while the ASM code uses JMP instruction to jump to the start of the first call site.
The complier uses tail-call-optimization for calling sync_regs(). It uses "JMP sync_regs" while the ASM code uses "CALL+RET".
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com> --- arch/x86/entry/entry64.c | 69 +++++++++++++++++++++++++++++ arch/x86/entry/entry_64.S | 85 ++---------------------------------- arch/x86/include/asm/proto.h | 1 + arch/x86/include/asm/traps.h | 1 + arch/x86/kernel/traps.c | 2 - 5 files changed, 74 insertions(+), 84 deletions(-)
diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c index f7f23800cee4..bd047c329622 100644 --- a/arch/x86/entry/entry64.c +++ b/arch/x86/entry/entry64.c @@ -13,6 +13,8 @@ */ #include <asm/traps.h> +extern unsigned char asm_load_gs_index_gs_change[]; + #ifdef CONFIG_PAGE_TABLE_ISOLATION static __always_inline void pti_switch_to_kernel_cr3(unsigned long user_cr3) { @@ -66,3 +68,70 @@ static __always_inline void user_entry_swapgs_and_fence(void) native_swapgs(); fence_swapgs_user_entry(); } + +/* + * Put pt_regs onto the task stack and switch GS and CR3 if needed. + * The actual stack switch is done in entry_64.S. + * + * Be careful, it might be in the user CR3 and user GS base at the start + * of the function. + */ +asmlinkage __visible __entry_text +struct pt_regs *error_entry(struct pt_regs *eregs) +{ + unsigned long iret_ip = (unsigned long)native_irq_return_iret; + + if (user_mode(eregs)) { + /* + * We entered from user mode. + * Switch to kernel gsbase and CR3. + */ + user_entry_swapgs_and_fence(); + switch_to_kernel_cr3(); + + /* Put pt_regs onto the task stack. */ + return sync_regs(eregs); + } + + /* + * There are two places in the kernel that can potentially fault with + * usergs. Handle them here. B stepping K8s sometimes report a + * truncated RIP for IRET exceptions returning to compat mode. Check + * for these here too. + */ + if ((eregs->ip == iret_ip) || (eregs->ip == (unsigned int)iret_ip)) { + eregs->ip = iret_ip; /* Fix truncated RIP */ + + /* + * We came from an IRET to user mode, so we have user + * gsbase and CR3. Switch to kernel gsbase and CR3: + */ + user_entry_swapgs_and_fence(); + switch_to_kernel_cr3(); + + /* + * Pretend that the exception came from user mode: set up + * pt_regs as if we faulted immediately after IRET and then + * put pt_regs onto the real task stack. + */ + return sync_regs(fixup_bad_iret(eregs)); + } + + /* + * Hack: asm_load_gs_index_gs_change can fail with user gsbase. + * If this happens, fix up gsbase and proceed. We'll fix up the + * exception and land in asm_load_gs_index_gs_change's error + * handler with kernel gsbase. + */ + if (eregs->ip == (unsigned long)asm_load_gs_index_gs_change) + native_swapgs(); + + /* + * Issue an LFENCE to prevent GS speculation, regardless of whether + * it is a kernel or user gsbase. + */ + fence_swapgs_kernel_entry(); + + /* Enter from kernel, don't move pt_regs */ + return eregs; +} diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 4300ba49b5ee..f8322398fe1c 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -348,7 +348,7 @@ SYM_CODE_END(push_and_clear_regs) * own pvops for IRET and load_gs_index(). And it doesn't need to * switch the CR3. So it can skip invoking error_entry(). */ - ALTERNATIVE "call error_entry; movq %rax, %rsp", \ + ALTERNATIVE "movq %rsp, %rdi; call error_entry; movq %rax, %rsp", \ "", X86_FEATURE_XENPV ENCODE_FRAME_POINTER @@ -784,7 +784,7 @@ _ASM_NOKPROBE(common_interrupt_return) SYM_FUNC_START(asm_load_gs_index) FRAME_BEGIN swapgs -.Lgs_change: +SYM_INNER_LABEL(asm_load_gs_index_gs_change, SYM_L_GLOBAL) ANNOTATE_NOENDBR // error_entry movl %edi, %gs 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE @@ -805,7 +805,7 @@ SYM_FUNC_START(asm_load_gs_index) movl %eax, %gs jmp 2b - _ASM_EXTABLE(.Lgs_change, .Lbad_gs) + _ASM_EXTABLE(asm_load_gs_index_gs_change, .Lbad_gs) SYM_FUNC_END(asm_load_gs_index) EXPORT_SYMBOL(asm_load_gs_index) @@ -1012,85 +1012,6 @@ SYM_CODE_START_LOCAL(paranoid_exit) jmp restore_regs_and_return_to_kernel SYM_CODE_END(paranoid_exit) -/* - * Switch GS and CR3 if needed. - */ -SYM_CODE_START_LOCAL(error_entry) - UNWIND_HINT_FUNC - testb $3, CS+8(%rsp) - jz .Lerror_kernelspace - - /* - * We entered from user mode or we're pretending to have entered - * from user mode due to an IRET fault. - */ - swapgs - FENCE_SWAPGS_USER_ENTRY - /* We have user CR3. Change to kernel CR3. */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%rax - - leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */ -.Lerror_entry_from_usermode_after_swapgs: - /* Put us onto the real thread stack. */ - call sync_regs - RET - - /* - * There are two places in the kernel that can potentially fault with - * usergs. Handle them here. B stepping K8s sometimes report a - * truncated RIP for IRET exceptions returning to compat mode. Check - * for these here too. - */ -.Lerror_kernelspace: - leaq native_irq_return_iret(%rip), %rcx - cmpq %rcx, RIP+8(%rsp) - je .Lerror_bad_iret - movl %ecx, %eax /* zero extend */ - cmpq %rax, RIP+8(%rsp) - je .Lbstep_iret - cmpq $.Lgs_change, RIP+8(%rsp) - jne .Lerror_entry_done_lfence - - /* - * hack: .Lgs_change can fail with user gsbase. If this happens, fix up - * gsbase and proceed. We'll fix up the exception and land in - * .Lgs_change's error handler with kernel gsbase. - */ - swapgs - - /* - * Issue an LFENCE to prevent GS speculation, regardless of whether it is a - * kernel or user gsbase. - */ -.Lerror_entry_done_lfence: - FENCE_SWAPGS_KERNEL_ENTRY - leaq 8(%rsp), %rax /* return pt_regs pointer */ - RET - -.Lbstep_iret: - /* Fix truncated RIP */ - movq %rcx, RIP+8(%rsp) - /* fall through */ - -.Lerror_bad_iret: - /* - * We came from an IRET to user mode, so we have user - * gsbase and CR3. Switch to kernel gsbase and CR3: - */ - swapgs - FENCE_SWAPGS_USER_ENTRY - SWITCH_TO_KERNEL_CR3 scratch_reg=%rax - - /* - * Pretend that the exception came from user mode: set up pt_regs - * as if we faulted immediately after IRET. - */ - leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */ - call fixup_bad_iret - mov %rax, %rdi - jmp .Lerror_entry_from_usermode_after_swapgs -SYM_CODE_END(error_entry) - SYM_CODE_START_LOCAL(error_return) UNWIND_HINT_REGS DEBUG_ENTRY_ASSERT_IRQS_OFF diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h index 12ef86b19910..199d27fbf903 100644 --- a/arch/x86/include/asm/proto.h +++ b/arch/x86/include/asm/proto.h @@ -15,6 +15,7 @@ void entry_SYSCALL_64(void); void entry_SYSCALL_64_safe_stack(void); void entry_SYSRETQ_unsafe_stack(void); void entry_SYSRETQ_end(void); +extern unsigned char native_irq_return_iret[]; long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2); #endif diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h index 47ecfff2c83d..2d00100d3e03 100644 --- a/arch/x86/include/asm/traps.h +++ b/arch/x86/include/asm/traps.h @@ -14,6 +14,7 @@ asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs); asmlinkage __visible notrace struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs); +asmlinkage __visible notrace struct pt_regs *error_entry(struct pt_regs *eregs); void __init trap_init(void); asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *eregs); #endif diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d62b2cb85cea..f76a15f654c5 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -436,8 +436,6 @@ DEFINE_IDTENTRY_DF(exc_double_fault) #endif #ifdef CONFIG_X86_ESPFIX64 - extern unsigned char native_irq_return_iret[]; - /* * If IRET takes a non-IST fault on the espfix64 stack, then we * end up promoting it to a doublefault. In that case, take -- 2.19.1.6.gb485710b
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