[RFC PATCH] sysrq: Show architectural registers

[Borislav Petkov <bp@xxxxxxxxx>]

From: Borislav Petkov <borislav.petkov@xxxxxxx>

One day I was playing with disabling the caches over CR0.CD and I wanted
to check the current setting of the CD bit but there wasn't a way to do
so from userspace because we #GP when accessing CR0.

And then I thought, well, sysrq must have this. And it does:

$ echo p > /proc/sysrq-trigger

dumps the current registers. However, we don't dump the registers when
we can't get the last exception frame through get_irq_regs().

But, there are registers (CR0 included) which aren't in the exception
frame and which can be dumped regardless. This patch does exactly that;
with it, the output looks like this:

[ 1759.206042] SysRq : Show Regs
[ 1759.209194] FS:  00007fb1eada3700(0000) GS:ffff880c27c00000(0000) knlGS:0000000000000000
[ 1759.217593] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1759.223554] CR2: 0000000000910390 CR3: 0000001020b48000 CR4: 00000000000007e0
[ 1759.230956] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1759.244974] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 1759.259052] CPU#18: active:     0000000000000000
[ 1759.270539] CPU#18:   gen-PMC0 ctrl:  0000030e011afcf6
[ 1759.270543] CPU#18:   gen-PMC0 count: 00009007d003b500
[ 1759.270545] CPU#18:   gen-PMC0 left:  0000000000000000
[ 1759.270548] CPU#18:   gen-PMC1 ctrl:  0000030f059b7efc
[ 1759.270550] CPU#18:   gen-PMC1 count: 00008003c823b4a0
[ 1759.270552] CPU#18:   gen-PMC1 left:  0000000000000000
[ 1759.270555] CPU#18:   gen-PMC2 ctrl:  00000104fe97c87c
[ 1759.270557] CPU#18:   gen-PMC2 count: 00007c6277e7f5fe
[ 1759.270560] CPU#18:   gen-PMC2 left:  0000000000000000
[ 1759.270562] CPU#18:   gen-PMC3 ctrl:  000000040000f0e2
[ 1759.270564] CPU#18:   gen-PMC3 count: 0000000000000000
[ 1759.270566] CPU#18:   gen-PMC3 left:  0000000000000000

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <borislav.petkov@xxxxxxx>
---
 arch/x86/include/asm/bug.h   |  3 +++
 arch/x86/kernel/process_32.c | 43 ++++++++++++++++++++++------------------
 arch/x86/kernel/process_64.c | 47 ++++++++++++++++++++++++--------------------
 drivers/tty/sysrq.c          |  1 +
 include/asm-generic/bug.h    |  9 +++++++++
 5 files changed, 63 insertions(+), 40 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 11e1152222d0..e60cf51fdfbd 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -35,6 +35,9 @@ do {								\
 
 #endif /* !CONFIG_BUG */
 
+extern void _arch_show_regs(void);
+#define _arch_show_regs _arch_show_regs
+
 #include <asm-generic/bug.h>
 
 
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 516fa186121b..6b01b6260f5d 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -66,10 +66,32 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
 	return ((unsigned long *)tsk->thread.sp)[3];
 }
 
-void __show_regs(struct pt_regs *regs, int all)
+void _arch_show_regs(void)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
 	unsigned long d0, d1, d2, d3, d6, d7;
+
+	cr0 = read_cr0();
+	cr2 = read_cr2();
+	cr3 = read_cr3();
+	cr4 = read_cr4_safe();
+	printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
+			cr0, cr2, cr3, cr4);
+
+	get_debugreg(d0, 0);
+	get_debugreg(d1, 1);
+	get_debugreg(d2, 2);
+	get_debugreg(d3, 3);
+	printk(KERN_DEFAULT "DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
+			d0, d1, d2, d3);
+
+	get_debugreg(d6, 6);
+	get_debugreg(d7, 7);
+	printk(KERN_DEFAULT "DR6: %08lx DR7: %08lx\n", d6, d7);
+}
+
+void __show_regs(struct pt_regs *regs, int all)
+{
 	unsigned long sp;
 	unsigned short ss, gs;
 
@@ -100,24 +122,7 @@ void __show_regs(struct pt_regs *regs, int all)
 	if (!all)
 		return;
 
-	cr0 = read_cr0();
-	cr2 = read_cr2();
-	cr3 = read_cr3();
-	cr4 = read_cr4_safe();
-	printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
-			cr0, cr2, cr3, cr4);
-
-	get_debugreg(d0, 0);
-	get_debugreg(d1, 1);
-	get_debugreg(d2, 2);
-	get_debugreg(d3, 3);
-	printk(KERN_DEFAULT "DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
-			d0, d1, d2, d3);
-
-	get_debugreg(d6, 6);
-	get_debugreg(d7, 7);
-	printk(KERN_DEFAULT "DR6: %08lx DR7: %08lx\n",
-			d6, d7);
+	_arch_show_regs();
 }
 
 void release_thread(struct task_struct *dead_task)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 0a980c9d7cb8..dbe93bae6524 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -54,30 +54,14 @@ asmlinkage extern void ret_from_fork(void);
 
 DEFINE_PER_CPU(unsigned long, old_rsp);
 
-/* Prints also some state that isn't saved in the pt_regs */
-void __show_regs(struct pt_regs *regs, int all)
+/* Print also some state that isn't saved in the pt_regs */
+void _arch_show_regs(void)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
 	unsigned long d0, d1, d2, d3, d6, d7;
 	unsigned int fsindex, gsindex;
 	unsigned int ds, cs, es;
 
-	show_regs_common();
-	printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] ", regs->cs & 0xffff, regs->ip);
-	printk_address(regs->ip, 1);
-	printk(KERN_DEFAULT "RSP: %04lx:%016lx  EFLAGS: %08lx\n", regs->ss,
-			regs->sp, regs->flags);
-	printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
-	       regs->ax, regs->bx, regs->cx);
-	printk(KERN_DEFAULT "RDX: %016lx RSI: %016lx RDI: %016lx\n",
-	       regs->dx, regs->si, regs->di);
-	printk(KERN_DEFAULT "RBP: %016lx R08: %016lx R09: %016lx\n",
-	       regs->bp, regs->r8, regs->r9);
-	printk(KERN_DEFAULT "R10: %016lx R11: %016lx R12: %016lx\n",
-	       regs->r10, regs->r11, regs->r12);
-	printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
-	       regs->r13, regs->r14, regs->r15);
-
 	asm("movl %%ds,%0" : "=r" (ds));
 	asm("movl %%cs,%0" : "=r" (cs));
 	asm("movl %%es,%0" : "=r" (es));
@@ -88,9 +72,6 @@ void __show_regs(struct pt_regs *regs, int all)
 	rdmsrl(MSR_GS_BASE, gs);
 	rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
 
-	if (!all)
-		return;
-
 	cr0 = read_cr0();
 	cr2 = read_cr2();
 	cr3 = read_cr3();
@@ -113,6 +94,30 @@ void __show_regs(struct pt_regs *regs, int all)
 	printk(KERN_DEFAULT "DR3: %016lx DR6: %016lx DR7: %016lx\n", d3, d6, d7);
 }
 
+void __show_regs(struct pt_regs *regs, int all)
+{
+	show_regs_common();
+	printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] ", regs->cs & 0xffff, regs->ip);
+	printk_address(regs->ip, 1);
+	printk(KERN_DEFAULT "RSP: %04lx:%016lx  EFLAGS: %08lx\n", regs->ss,
+			regs->sp, regs->flags);
+	printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
+	       regs->ax, regs->bx, regs->cx);
+	printk(KERN_DEFAULT "RDX: %016lx RSI: %016lx RDI: %016lx\n",
+	       regs->dx, regs->si, regs->di);
+	printk(KERN_DEFAULT "RBP: %016lx R08: %016lx R09: %016lx\n",
+	       regs->bp, regs->r8, regs->r9);
+	printk(KERN_DEFAULT "R10: %016lx R11: %016lx R12: %016lx\n",
+	       regs->r10, regs->r11, regs->r12);
+	printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
+	       regs->r13, regs->r14, regs->r15);
+
+	if (!all)
+		return;
+
+	_arch_show_regs();
+}
+
 void release_thread(struct task_struct *dead_task)
 {
 	if (dead_task->mm) {
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 05728894a88c..4ad0f884e08e 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -254,6 +254,7 @@ static void sysrq_handle_showregs(int key)
 	struct pt_regs *regs = get_irq_regs();
 	if (regs)
 		show_regs(regs);
+	arch_show_regs();
 	perf_event_print_debug();
 }
 static struct sysrq_key_op sysrq_showregs_op = {
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 7d10f962aa13..e96d6c31c222 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -202,6 +202,15 @@ extern void warn_slowpath_null(const char *file, const int line);
 # define WARN_ON_SMP(x)			({0;})
 #endif
 
+#ifdef _arch_show_regs
+static inline void arch_show_regs(void)
+{
+	_arch_show_regs();
+}
+#else
+static inline void arch_show_regs(void) { }
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif
-- 
1.7.11.rc1

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