From 5b06bbcfc2c621da3009da8decb7511500c293ed Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 30 Nov 2017 07:57:57 -0800 Subject: x86/power: Fix some ordering bugs in __restore_processor_context() __restore_processor_context() had a couple of ordering bugs. It restored GSBASE after calling load_gs_index(), and the latter can call into tracing code. It also tried to restore segment registers before restoring the LDT, which is straight-up wrong. Reorder the code so that we restore GSBASE, then the descriptor tables, then the segments. This fixes two bugs. First, it fixes a regression that broke resume under certain configurations due to irqflag tracing in native_load_gs_index(). Second, it fixes resume when the userspace process that initiated suspect had funny segments. The latter can be reproduced by compiling this: // SPDX-License-Identifier: GPL-2.0 /* * ldt_echo.c - Echo argv[1] while using an LDT segment */ int main(int argc, char **argv) { int ret; size_t len; char *buf; const struct user_desc desc = { .entry_number = 0, .base_addr = 0, .limit = 0xfffff, .seg_32bit = 1, .contents = 0, /* Data, grow-up */ .read_exec_only = 0, .limit_in_pages = 1, .seg_not_present = 0, .useable = 0 }; if (argc != 2) errx(1, "Usage: %s STRING", argv[0]); len = asprintf(&buf, "%s\n", argv[1]); if (len < 0) errx(1, "Out of memory"); ret = syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)); if (ret < -1) errno = -ret; if (ret) err(1, "modify_ldt"); asm volatile ("movw %0, %%es" :: "rm" ((unsigned short)7)); write(1, buf, len); return 0; } and running ldt_echo >/sys/power/mem Without the fix, the latter causes a triple fault on resume. Fixes: ca37e57bbe0c ("x86/entry/64: Add missing irqflags tracing to native_load_gs_index()") Reported-by: Jarkko Nikula Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Tested-by: Jarkko Nikula Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Linus Torvalds Link: https://lkml.kernel.org/r/6b31721ea92f51ea839e79bd97ade4a75b1eeea2.1512057304.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/power/cpu.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) (limited to 'arch/x86/power') diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c index 84fcfde53f8f..5191de14f4df 100644 --- a/arch/x86/power/cpu.c +++ b/arch/x86/power/cpu.c @@ -226,8 +226,20 @@ static void notrace __restore_processor_state(struct saved_context *ctxt) load_idt((const struct desc_ptr *)&ctxt->idt_limit); #endif +#ifdef CONFIG_X86_64 /* - * segment registers + * We need GSBASE restored before percpu access can work. + * percpu access can happen in exception handlers or in complicated + * helpers like load_gs_index(). + */ + wrmsrl(MSR_GS_BASE, ctxt->gs_base); +#endif + + fix_processor_context(); + + /* + * Restore segment registers. This happens after restoring the GDT + * and LDT, which happen in fix_processor_context(). */ #ifdef CONFIG_X86_32 loadsegment(es, ctxt->es); @@ -248,13 +260,14 @@ static void notrace __restore_processor_state(struct saved_context *ctxt) load_gs_index(ctxt->gs); asm volatile ("movw %0, %%ss" :: "r" (ctxt->ss)); + /* + * Restore FSBASE and user GSBASE after reloading the respective + * segment selectors. + */ wrmsrl(MSR_FS_BASE, ctxt->fs_base); - wrmsrl(MSR_GS_BASE, ctxt->gs_base); wrmsrl(MSR_KERNEL_GS_BASE, ctxt->gs_kernel_base); #endif - fix_processor_context(); - do_fpu_end(); tsc_verify_tsc_adjust(true); x86_platform.restore_sched_clock_state(); -- cgit v1.2.3