From: Ville Syrjälä ville.syrjala@linux.intel.com

APM_DO_POP_SEGS does not restore fs/gs which were zeroed by APM_DO_ZERO_SEGS. Trying to access __preempt_count with zeroed fs doesn't really work. Move the ibrs stuff outside the APM_DO_SAVE_SEGS/APM_DO_RESTORE_SEGS invocations so that fs is actually restored before we call preempt_enable().

Fixes the following sort of oopses: [ 0.313581] general protection fault: 0000 [#1] PREEMPT SMP [ 0.313803] Modules linked in: [ 0.314040] CPU: 0 PID: 268 Comm: kapmd Not tainted 4.16.0-rc1-triton-bisect-00090-gdd84441a7971 #19 [ 0.316161] EIP: __apm_bios_call_simple+0xc8/0x170 [ 0.316161] EFLAGS: 00210016 CPU: 0 [ 0.316161] EAX: 00000102 EBX: 00000000 ECX: 00000102 EDX: 00000000 [ 0.316161] ESI: 0000530e EDI: dea95f64 EBP: dea95f18 ESP: dea95ef0 [ 0.316161] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 [ 0.316161] CR0: 80050033 CR2: 00000000 CR3: 015d3000 CR4: 000006d0 [ 0.316161] Call Trace: [ 0.316161] ? cpumask_weight.constprop.15+0x20/0x20 [ 0.316161] on_cpu0+0x44/0x70 [ 0.316161] apm+0x54e/0x720 [ 0.316161] ? __switch_to_asm+0x26/0x40 [ 0.316161] ? __schedule+0x17d/0x590 [ 0.316161] kthread+0xc0/0xf0 [ 0.316161] ? proc_apm_show+0x150/0x150 [ 0.316161] ? kthread_create_worker_on_cpu+0x20/0x20 [ 0.316161] ret_from_fork+0x2e/0x38 [ 0.316161] Code: da 8e c2 8e e2 8e ea 57 55 2e ff 1d e0 bb 5d b1 0f 92 c3 5d 5f 07 1f 89 47 0c 90 8d b4 26 00 00 00 00 90 8d b4 26 00 00 00 00 90 <64> ff 0d 84 16 5c b1 74 7f 8b 45 dc 8e e0 8b 45 d8 8e e8 8b 45 [ 0.316161] EIP: __apm_bios_call_simple+0xc8/0x170 SS:ESP: 0068:dea95ef0 [ 0.316161] ---[ end trace 656253db2deaa12c ]---

Cc: stable@vger.kernel.org Cc: David Woodhouse dwmw@amazon.co.uk Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: x86@kernel.org Fixes: dd84441a7971 ("x86/speculation: Use IBRS if available before calling into firmware") Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com --- arch/x86/include/asm/apm.h | 6 ------ arch/x86/kernel/apm_32.c | 5 +++++ 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/apm.h b/arch/x86/include/asm/apm.h index c356098b6fb9..4d4015ddcf26 100644 --- a/arch/x86/include/asm/apm.h +++ b/arch/x86/include/asm/apm.h @@ -7,8 +7,6 @@ #ifndef _ASM_X86_MACH_DEFAULT_APM_H #define _ASM_X86_MACH_DEFAULT_APM_H

-#include <asm/nospec-branch.h> - #ifdef APM_ZERO_SEGS # define APM_DO_ZERO_SEGS \ "pushl %%ds\n\t" \ @@ -34,7 +32,6 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in, * N.B. We do NOT need a cld after the BIOS call * because we always save and restore the flags. */ - firmware_restrict_branch_speculation_start(); __asm__ __volatile__(APM_DO_ZERO_SEGS "pushl %%edi\n\t" "pushl %%ebp\n\t" @@ -47,7 +44,6 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in, "=S" (*esi) : "a" (func), "b" (ebx_in), "c" (ecx_in) : "memory", "cc"); - firmware_restrict_branch_speculation_end(); }

static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in, @@ -60,7 +56,6 @@ static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in, * N.B. We do NOT need a cld after the BIOS call * because we always save and restore the flags. */ - firmware_restrict_branch_speculation_start(); __asm__ __volatile__(APM_DO_ZERO_SEGS "pushl %%edi\n\t" "pushl %%ebp\n\t" @@ -73,7 +68,6 @@ static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in, "=S" (si) : "a" (func), "b" (ebx_in), "c" (ecx_in) : "memory", "cc"); - firmware_restrict_branch_speculation_end(); return error; }

diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c index 5d0de79fdab0..ec00d1ff5098 100644 --- a/arch/x86/kernel/apm_32.c +++ b/arch/x86/kernel/apm_32.c @@ -240,6 +240,7 @@ #include <asm/olpc.h> #include <asm/paravirt.h> #include <asm/reboot.h> +#include <asm/nospec-branch.h>

#if defined(CONFIG_APM_DISPLAY_BLANK) && defined(CONFIG_VT) extern int (*console_blank_hook)(int); @@ -614,11 +615,13 @@ static long __apm_bios_call(void *_call) gdt[0x40 / 8] = bad_bios_desc;

apm_irq_save(flags); + firmware_restrict_branch_speculation_start(); APM_DO_SAVE_SEGS; apm_bios_call_asm(call->func, call->ebx, call->ecx, &call->eax, &call->ebx, &call->ecx, &call->edx, &call->esi); APM_DO_RESTORE_SEGS; + firmware_restrict_branch_speculation_end(); apm_irq_restore(flags); gdt[0x40 / 8] = save_desc_40; put_cpu(); @@ -690,10 +693,12 @@ static long __apm_bios_call_simple(void *_call) gdt[0x40 / 8] = bad_bios_desc;

apm_irq_save(flags); + firmware_restrict_branch_speculation_start(); APM_DO_SAVE_SEGS; error = apm_bios_call_simple_asm(call->func, call->ebx, call->ecx, &call->eax); APM_DO_RESTORE_SEGS; + firmware_restrict_branch_speculation_end(); apm_irq_restore(flags); gdt[0x40 / 8] = save_desc_40; put_cpu();