[PATCH] x86/process: don't mix user/kernel regs in 64bit __show_regs

[PATCH] x86/process: don't mix user/kernel regs in 64bit __show_regs

[Jann Horn]

When the kernel.print-fatal-signals sysctl has been enabled (I don't know
whether anyone actually enables it), a simple userspace crash will cause
the kernel to write a crash dump that contains, among other things, the
kernel gsbase into dmesg.

As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
in this case.

This also moves the bitness-specific logic from show_regs() into
process_{32,64}.c.

Signed-off-by: Jann Horn <jannh@google.com>
Fixes: 45807a1df9f5 ("vdso: print fatal signals")
---
@Andy: Does this look like what you had in mind?

Does this need a CC stable tag? I haven't put one on it for now.

 arch/x86/include/asm/kdebug.h | 12 +++++++++++-
 arch/x86/kernel/dumpstack.c   | 11 +++--------
 arch/x86/kernel/process_32.c  |  4 ++--
 arch/x86/kernel/process_64.c  | 12 ++++++++++--
 4 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h
index 395c9631e000..75f1e35e7c15 100644
--- a/arch/x86/include/asm/kdebug.h
+++ b/arch/x86/include/asm/kdebug.h
@@ -22,10 +22,20 @@ enum die_val {
 	DIE_NMIUNKNOWN,
 };
 
+enum show_regs_mode {
+	SHOW_REGS_SHORT,
+	/*
+	 * For when userspace crashed, but we don't think it's our fault, and
+	 * therefore don't print kernel registers.
+	 */
+	SHOW_REGS_USER,
+	SHOW_REGS_ALL
+};
+
 extern void die(const char *, struct pt_regs *,long);
 extern int __must_check __die(const char *, struct pt_regs *, long);
 extern void show_stack_regs(struct pt_regs *regs);
-extern void __show_regs(struct pt_regs *regs, int all);
+extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
 extern void show_iret_regs(struct pt_regs *regs);
 extern unsigned long oops_begin(void);
 extern void oops_end(unsigned long, struct pt_regs *, int signr);
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 9c8652974f8e..574fe5d97ba2 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -135,7 +135,7 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
 	 * they can be printed in the right context.
 	 */
 	if (!partial && on_stack(info, regs, sizeof(*regs))) {
-		__show_regs(regs, 0);
+		__show_regs(regs, SHOW_REGS_SHORT);
 
 	} else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
 				       IRET_FRAME_SIZE)) {
@@ -333,7 +333,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 	oops_exit();
 
 	/* Executive summary in case the oops scrolled away */
-	__show_regs(&exec_summary_regs, true);
+	__show_regs(&exec_summary_regs, SHOW_REGS_ALL);
 
 	if (!signr)
 		return;
@@ -393,14 +393,9 @@ void die(const char *str, struct pt_regs *regs, long err)
 
 void show_regs(struct pt_regs *regs)
 {
-	bool all = true;
-
 	show_regs_print_info(KERN_DEFAULT);
 
-	if (IS_ENABLED(CONFIG_X86_32))
-		all = !user_mode(regs);
-
-	__show_regs(regs, all);
+	__show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);
 
 	/*
 	 * When in-kernel, we also print out the stack at the time of the fault..
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 2924fd447e61..5046a3c9dec2 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -59,7 +59,7 @@
 #include <asm/intel_rdt_sched.h>
 #include <asm/proto.h>
 
-void __show_regs(struct pt_regs *regs, int all)
+void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 	unsigned long d0, d1, d2, d3, d6, d7;
@@ -85,7 +85,7 @@ void __show_regs(struct pt_regs *regs, int all)
 	printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
 	       (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);
 
-	if (!all)
+	if (mode != SHOW_REGS_ALL)
 		return;
 
 	cr0 = read_cr0();
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index a451bc374b9b..ea5ea850348d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -62,7 +62,7 @@
 __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
 
 /* Prints also some state that isn't saved in the pt_regs */
-void __show_regs(struct pt_regs *regs, int all)
+void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
 	unsigned long d0, d1, d2, d3, d6, d7;
@@ -87,9 +87,17 @@ void __show_regs(struct pt_regs *regs, int all)
 	printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
 	       regs->r13, regs->r14, regs->r15);
 
-	if (!all)
+	if (mode == SHOW_REGS_SHORT)
 		return;
 
+	if (mode == SHOW_REGS_USER) {
+		rdmsrl(MSR_FS_BASE, fs);
+		rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
+		printk(KERN_DEFAULT "FS:  %016lx GS:  %016lx\n",
+		       fs, shadowgs);
+		return;
+	}
+
 	asm("movl %%ds,%0" : "=r" (ds));
 	asm("movl %%cs,%0" : "=r" (cs));
 	asm("movl %%es,%0" : "=r" (es));
-- 
2.19.0.rc1.350.ge57e33dbd1-goog

Re: [PATCH] x86/process: don't mix user/kernel regs in 64bit __show_regs

[Andy Lutomirski]

On Fri, Aug 31, 2018 at 12:41 PM, Jann Horn <jannh@google.com> wrote:
> When the kernel.print-fatal-signals sysctl has been enabled (I don't know
> whether anyone actually enables it), a simple userspace crash will cause
> the kernel to write a crash dump that contains, among other things, the
> kernel gsbase into dmesg.
>
> As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
> in this case.
>
> This also moves the bitness-specific logic from show_regs() into
> process_{32,64}.c.
>
> Signed-off-by: Jann Horn <jannh@google.com>
> Fixes: 45807a1df9f5 ("vdso: print fatal signals")
> ---
> @Andy: Does this look like what you had in mind?

Yes.

Although there's another option: remove print-fatal-signals.

>
> Does this need a CC stable tag? I haven't put one on it for now.

Probably.

>
>  arch/x86/include/asm/kdebug.h | 12 +++++++++++-
>  arch/x86/kernel/dumpstack.c   | 11 +++--------
>  arch/x86/kernel/process_32.c  |  4 ++--
>  arch/x86/kernel/process_64.c  | 12 ++++++++++--
>  4 files changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h
> index 395c9631e000..75f1e35e7c15 100644
> --- a/arch/x86/include/asm/kdebug.h
> +++ b/arch/x86/include/asm/kdebug.h
> @@ -22,10 +22,20 @@ enum die_val {
>         DIE_NMIUNKNOWN,
>  };
>
> +enum show_regs_mode {
> +       SHOW_REGS_SHORT,
> +       /*
> +        * For when userspace crashed, but we don't think it's our fault, and
> +        * therefore don't print kernel registers.
> +        */
> +       SHOW_REGS_USER,
> +       SHOW_REGS_ALL
> +};
> +
>  extern void die(const char *, struct pt_regs *,long);
>  extern int __must_check __die(const char *, struct pt_regs *, long);
>  extern void show_stack_regs(struct pt_regs *regs);
> -extern void __show_regs(struct pt_regs *regs, int all);
> +extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
>  extern void show_iret_regs(struct pt_regs *regs);
>  extern unsigned long oops_begin(void);
>  extern void oops_end(unsigned long, struct pt_regs *, int signr);
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 9c8652974f8e..574fe5d97ba2 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -135,7 +135,7 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
>          * they can be printed in the right context.
>          */
>         if (!partial && on_stack(info, regs, sizeof(*regs))) {
> -               __show_regs(regs, 0);
> +               __show_regs(regs, SHOW_REGS_SHORT);
>
>         } else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
>                                        IRET_FRAME_SIZE)) {
> @@ -333,7 +333,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
>         oops_exit();
>
>         /* Executive summary in case the oops scrolled away */
> -       __show_regs(&exec_summary_regs, true);
> +       __show_regs(&exec_summary_regs, SHOW_REGS_ALL);
>
>         if (!signr)
>                 return;
> @@ -393,14 +393,9 @@ void die(const char *str, struct pt_regs *regs, long err)
>
>  void show_regs(struct pt_regs *regs)
>  {
> -       bool all = true;
> -
>         show_regs_print_info(KERN_DEFAULT);
>
> -       if (IS_ENABLED(CONFIG_X86_32))
> -               all = !user_mode(regs);
> -
> -       __show_regs(regs, all);
> +       __show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);
>
>         /*
>          * When in-kernel, we also print out the stack at the time of the fault..
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 2924fd447e61..5046a3c9dec2 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -59,7 +59,7 @@
>  #include <asm/intel_rdt_sched.h>
>  #include <asm/proto.h>
>
> -void __show_regs(struct pt_regs *regs, int all)
> +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
>  {
>         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
>         unsigned long d0, d1, d2, d3, d6, d7;
> @@ -85,7 +85,7 @@ void __show_regs(struct pt_regs *regs, int all)
>         printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
>                (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);
>
> -       if (!all)
> +       if (mode != SHOW_REGS_ALL)
>                 return;
>
>         cr0 = read_cr0();
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index a451bc374b9b..ea5ea850348d 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -62,7 +62,7 @@
>  __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
>
>  /* Prints also some state that isn't saved in the pt_regs */
> -void __show_regs(struct pt_regs *regs, int all)
> +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
>  {
>         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
>         unsigned long d0, d1, d2, d3, d6, d7;
> @@ -87,9 +87,17 @@ void __show_regs(struct pt_regs *regs, int all)
>         printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
>                regs->r13, regs->r14, regs->r15);
>
> -       if (!all)
> +       if (mode == SHOW_REGS_SHORT)
>                 return;
>
> +       if (mode == SHOW_REGS_USER) {
> +               rdmsrl(MSR_FS_BASE, fs);
> +               rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
> +               printk(KERN_DEFAULT "FS:  %016lx GS:  %016lx\n",
> +                      fs, shadowgs);
> +               return;
> +       }
> +
>         asm("movl %%ds,%0" : "=r" (ds));
>         asm("movl %%cs,%0" : "=r" (cs));
>         asm("movl %%es,%0" : "=r" (es));
> --
> 2.19.0.rc1.350.ge57e33dbd1-goog
>

Re: [PATCH] x86/process: don't mix user/kernel regs in 64bit __show_regs

[Jann Horn]

On Fri, Aug 31, 2018 at 10:12 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Fri, Aug 31, 2018 at 12:41 PM, Jann Horn <jannh@google.com> wrote:
> > When the kernel.print-fatal-signals sysctl has been enabled (I don't know
> > whether anyone actually enables it), a simple userspace crash will cause
> > the kernel to write a crash dump that contains, among other things, the
> > kernel gsbase into dmesg.
> >
> > As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
> > in this case.
> >
> > This also moves the bitness-specific logic from show_regs() into
> > process_{32,64}.c.
> >
> > Signed-off-by: Jann Horn <jannh@google.com>
> > Fixes: 45807a1df9f5 ("vdso: print fatal signals")
> > ---
> > @Andy: Does this look like what you had in mind?
>
> Yes.
>
> Although there's another option: remove print-fatal-signals.

Who wants to decide? Ingo, it's your feature - what do you think?

> > Does this need a CC stable tag? I haven't put one on it for now.
>
> Probably.
>
> >
> >  arch/x86/include/asm/kdebug.h | 12 +++++++++++-
> >  arch/x86/kernel/dumpstack.c   | 11 +++--------
> >  arch/x86/kernel/process_32.c  |  4 ++--
> >  arch/x86/kernel/process_64.c  | 12 ++++++++++--
> >  4 files changed, 26 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h
> > index 395c9631e000..75f1e35e7c15 100644
> > --- a/arch/x86/include/asm/kdebug.h
> > +++ b/arch/x86/include/asm/kdebug.h
> > @@ -22,10 +22,20 @@ enum die_val {
> >         DIE_NMIUNKNOWN,
> >  };
> >
> > +enum show_regs_mode {
> > +       SHOW_REGS_SHORT,
> > +       /*
> > +        * For when userspace crashed, but we don't think it's our fault, and
> > +        * therefore don't print kernel registers.
> > +        */
> > +       SHOW_REGS_USER,
> > +       SHOW_REGS_ALL
> > +};
> > +
> >  extern void die(const char *, struct pt_regs *,long);
> >  extern int __must_check __die(const char *, struct pt_regs *, long);
> >  extern void show_stack_regs(struct pt_regs *regs);
> > -extern void __show_regs(struct pt_regs *regs, int all);
> > +extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
> >  extern void show_iret_regs(struct pt_regs *regs);
> >  extern unsigned long oops_begin(void);
> >  extern void oops_end(unsigned long, struct pt_regs *, int signr);
> > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> > index 9c8652974f8e..574fe5d97ba2 100644
> > --- a/arch/x86/kernel/dumpstack.c
> > +++ b/arch/x86/kernel/dumpstack.c
> > @@ -135,7 +135,7 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
> >          * they can be printed in the right context.
> >          */
> >         if (!partial && on_stack(info, regs, sizeof(*regs))) {
> > -               __show_regs(regs, 0);
> > +               __show_regs(regs, SHOW_REGS_SHORT);
> >
> >         } else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
> >                                        IRET_FRAME_SIZE)) {
> > @@ -333,7 +333,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
> >         oops_exit();
> >
> >         /* Executive summary in case the oops scrolled away */
> > -       __show_regs(&exec_summary_regs, true);
> > +       __show_regs(&exec_summary_regs, SHOW_REGS_ALL);
> >
> >         if (!signr)
> >                 return;
> > @@ -393,14 +393,9 @@ void die(const char *str, struct pt_regs *regs, long err)
> >
> >  void show_regs(struct pt_regs *regs)
> >  {
> > -       bool all = true;
> > -
> >         show_regs_print_info(KERN_DEFAULT);
> >
> > -       if (IS_ENABLED(CONFIG_X86_32))
> > -               all = !user_mode(regs);
> > -
> > -       __show_regs(regs, all);
> > +       __show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);
> >
> >         /*
> >          * When in-kernel, we also print out the stack at the time of the fault..
> > diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> > index 2924fd447e61..5046a3c9dec2 100644
> > --- a/arch/x86/kernel/process_32.c
> > +++ b/arch/x86/kernel/process_32.c
> > @@ -59,7 +59,7 @@
> >  #include <asm/intel_rdt_sched.h>
> >  #include <asm/proto.h>
> >
> > -void __show_regs(struct pt_regs *regs, int all)
> > +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
> >  {
> >         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
> >         unsigned long d0, d1, d2, d3, d6, d7;
> > @@ -85,7 +85,7 @@ void __show_regs(struct pt_regs *regs, int all)
> >         printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
> >                (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);
> >
> > -       if (!all)
> > +       if (mode != SHOW_REGS_ALL)
> >                 return;
> >
> >         cr0 = read_cr0();
> > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> > index a451bc374b9b..ea5ea850348d 100644
> > --- a/arch/x86/kernel/process_64.c
> > +++ b/arch/x86/kernel/process_64.c
> > @@ -62,7 +62,7 @@
> >  __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
> >
> >  /* Prints also some state that isn't saved in the pt_regs */
> > -void __show_regs(struct pt_regs *regs, int all)
> > +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
> >  {
> >         unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
> >         unsigned long d0, d1, d2, d3, d6, d7;
> > @@ -87,9 +87,17 @@ void __show_regs(struct pt_regs *regs, int all)
> >         printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
> >                regs->r13, regs->r14, regs->r15);
> >
> > -       if (!all)
> > +       if (mode == SHOW_REGS_SHORT)
> >                 return;
> >
> > +       if (mode == SHOW_REGS_USER) {
> > +               rdmsrl(MSR_FS_BASE, fs);
> > +               rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
> > +               printk(KERN_DEFAULT "FS:  %016lx GS:  %016lx\n",
> > +                      fs, shadowgs);
> > +               return;
> > +       }
> > +
> >         asm("movl %%ds,%0" : "=r" (ds));
> >         asm("movl %%cs,%0" : "=r" (cs));
> >         asm("movl %%es,%0" : "=r" (es));
> > --
> > 2.19.0.rc1.350.ge57e33dbd1-goog
> >

Re: [PATCH] x86/process: don't mix user/kernel regs in 64bit __show_regs

[Thomas Gleixner]

On Thu, 6 Sep 2018, Jann Horn wrote:
> On Fri, Aug 31, 2018 at 10:12 PM Andy Lutomirski <luto@kernel.org> wrote:
> >
> > On Fri, Aug 31, 2018 at 12:41 PM, Jann Horn <jannh@google.com> wrote:
> > > When the kernel.print-fatal-signals sysctl has been enabled (I don't know
> > > whether anyone actually enables it), a simple userspace crash will cause
> > > the kernel to write a crash dump that contains, among other things, the
> > > kernel gsbase into dmesg.
> > >
> > > As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
> > > in this case.
> > >
> > > This also moves the bitness-specific logic from show_regs() into
> > > process_{32,64}.c.
> > >
> > > Signed-off-by: Jann Horn <jannh@google.com>
> > > Fixes: 45807a1df9f5 ("vdso: print fatal signals")
> > > ---
> > > @Andy: Does this look like what you had in mind?
> >
> > Yes.
> >
> > Although there's another option: remove print-fatal-signals.
> 
> Who wants to decide? Ingo, it's your feature - what do you think?

It seems to be documented for trouble shooting in lots of places and the
fix is not horrible. So lets keep it.

Thanks,

	tglx

[tip:x86/urgent] x86/process: Don't mix user/kernel regs in 64bit __show_regs()

[tip-bot for Jann Horn]

Commit-ID:  9fe6299dde587788f245e9f7a5a1b296fad4e8c7
Gitweb:     https://git.kernel.org/tip/9fe6299dde587788f245e9f7a5a1b296fad4e8c7
Author:     Jann Horn <jannh@google.com>
AuthorDate: Fri, 31 Aug 2018 21:41:51 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 6 Sep 2018 14:33:12 +0200

x86/process: Don't mix user/kernel regs in 64bit __show_regs()

When the kernel.print-fatal-signals sysctl has been enabled, a simple
userspace crash will cause the kernel to write a crash dump that contains,
among other things, the kernel gsbase into dmesg.

As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
in this case.

This also moves the bitness-specific logic from show_regs() into
process_{32,64}.c.

Fixes: 45807a1df9f5 ("vdso: print fatal signals")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180831194151.123586-1-jannh@google.com

---
 arch/x86/include/asm/kdebug.h | 12 +++++++++++-
 arch/x86/kernel/dumpstack.c   | 11 +++--------
 arch/x86/kernel/process_32.c  |  4 ++--
 arch/x86/kernel/process_64.c  | 12 ++++++++++--
 4 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h
index 395c9631e000..75f1e35e7c15 100644
--- a/arch/x86/include/asm/kdebug.h
+++ b/arch/x86/include/asm/kdebug.h
@@ -22,10 +22,20 @@ enum die_val {
 	DIE_NMIUNKNOWN,
 };
 
+enum show_regs_mode {
+	SHOW_REGS_SHORT,
+	/*
+	 * For when userspace crashed, but we don't think it's our fault, and
+	 * therefore don't print kernel registers.
+	 */
+	SHOW_REGS_USER,
+	SHOW_REGS_ALL
+};
+
 extern void die(const char *, struct pt_regs *,long);
 extern int __must_check __die(const char *, struct pt_regs *, long);
 extern void show_stack_regs(struct pt_regs *regs);
-extern void __show_regs(struct pt_regs *regs, int all);
+extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
 extern void show_iret_regs(struct pt_regs *regs);
 extern unsigned long oops_begin(void);
 extern void oops_end(unsigned long, struct pt_regs *, int signr);
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index f56895106ccf..2b5886401e5f 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -146,7 +146,7 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
 	 * they can be printed in the right context.
 	 */
 	if (!partial && on_stack(info, regs, sizeof(*regs))) {
-		__show_regs(regs, 0);
+		__show_regs(regs, SHOW_REGS_SHORT);
 
 	} else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
 				       IRET_FRAME_SIZE)) {
@@ -344,7 +344,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 	oops_exit();
 
 	/* Executive summary in case the oops scrolled away */
-	__show_regs(&exec_summary_regs, true);
+	__show_regs(&exec_summary_regs, SHOW_REGS_ALL);
 
 	if (!signr)
 		return;
@@ -407,14 +407,9 @@ void die(const char *str, struct pt_regs *regs, long err)
 
 void show_regs(struct pt_regs *regs)
 {
-	bool all = true;
-
 	show_regs_print_info(KERN_DEFAULT);
 
-	if (IS_ENABLED(CONFIG_X86_32))
-		all = !user_mode(regs);
-
-	__show_regs(regs, all);
+	__show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);
 
 	/*
 	 * When in-kernel, we also print out the stack at the time of the fault..
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 2924fd447e61..5046a3c9dec2 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -59,7 +59,7 @@
 #include <asm/intel_rdt_sched.h>
 #include <asm/proto.h>
 
-void __show_regs(struct pt_regs *regs, int all)
+void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 	unsigned long d0, d1, d2, d3, d6, d7;
@@ -85,7 +85,7 @@ void __show_regs(struct pt_regs *regs, int all)
 	printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
 	       (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);
 
-	if (!all)
+	if (mode != SHOW_REGS_ALL)
 		return;
 
 	cr0 = read_cr0();
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index a451bc374b9b..ea5ea850348d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -62,7 +62,7 @@
 __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
 
 /* Prints also some state that isn't saved in the pt_regs */
-void __show_regs(struct pt_regs *regs, int all)
+void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
 	unsigned long d0, d1, d2, d3, d6, d7;
@@ -87,9 +87,17 @@ void __show_regs(struct pt_regs *regs, int all)
 	printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
 	       regs->r13, regs->r14, regs->r15);
 
-	if (!all)
+	if (mode == SHOW_REGS_SHORT)
 		return;
 
+	if (mode == SHOW_REGS_USER) {
+		rdmsrl(MSR_FS_BASE, fs);
+		rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
+		printk(KERN_DEFAULT "FS:  %016lx GS:  %016lx\n",
+		       fs, shadowgs);
+		return;
+	}
+
 	asm("movl %%ds,%0" : "=r" (ds));
 	asm("movl %%cs,%0" : "=r" (cs));
 	asm("movl %%es,%0" : "=r" (es));