[ PATCH 2/4] UML - Kernel segfaults should dump proper registers

From: Jeff Dike
Date: Wed Apr 04 2007 - 20:39:56 EST

If there's a segfault inside the kernel, we want a dump of the registers
at the point of the segfault, not the registers at the point of
calling panic or the last userspace registers.

sig_handler_common_skas now uses a static register set in the case
of a SIGSEGV to avoid messing up the process registers if the
segfault turns out to be non-fatal.

The architecture sigcontext-to-pt_regs copying code was repurposed
to copy data out of the SEGV stack frame.

Signed-off-by: Jeff Dike <jdike@xxxxxxxxxxxxxxx>
--
arch/um/include/common-offsets.h | 2 +
arch/um/include/kern_util.h | 2 +
arch/um/kernel/trap.c | 10 ++++++---
arch/um/os-Linux/skas/trap.c | 15 ++++++++++++--
arch/um/sys-i386/signal.c | 41 ++++++++++++++++++++++-----------------
arch/um/sys-x86_64/signal.c | 30 ++++++++++++++++++++++++++++
6 files changed, 78 insertions(+), 22 deletions(-)

Index: linux-2.6.21-mm/arch/um/kernel/trap.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/kernel/trap.c 2007-04-02 12:19:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/kernel/trap.c 2007-04-02 12:19:07.000000000 -0400
@@ -170,8 +170,10 @@ unsigned long segv(struct faultinfo fi,
flush_tlb_kernel_vm();
return 0;
}
- else if(current->mm == NULL)
- panic("Segfault with no mm");
+ else if(current->mm == NULL) {
+ show_regs(container_of(regs, struct pt_regs, regs));
+ panic("Segfault with no mm");
+ }

if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
err = handle_page_fault(address, ip, is_write, is_user, &si.si_code);
@@ -194,9 +196,11 @@ unsigned long segv(struct faultinfo fi,
else if(!is_user && arch_fixup(ip, regs))
return 0;

- if(!is_user)
+ if(!is_user) {
+ show_regs(container_of(regs, struct pt_regs, regs));
panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
address, ip);
+ }

if (err == -EACCES) {
si.si_signo = SIGBUS;
Index: linux-2.6.21-mm/arch/um/include/kern_util.h
===================================================================
--- linux-2.6.21-mm.orig/arch/um/include/kern_util.h 2007-04-02 12:19:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/include/kern_util.h 2007-04-02 12:19:07.000000000 -0400
@@ -116,4 +116,6 @@ extern void log_info(char *fmt, ...) __a
extern int __cant_sleep(void);
extern void sigio_handler(int sig, union uml_pt_regs *regs);

+extern void copy_sc(union uml_pt_regs *regs, void *from);
+
#endif
Index: linux-2.6.21-mm/arch/um/include/common-offsets.h
===================================================================
--- linux-2.6.21-mm.orig/arch/um/include/common-offsets.h 2007-04-02 12:18:49.000000000 -0400
+++ linux-2.6.21-mm/arch/um/include/common-offsets.h 2007-04-02 12:19:07.000000000 -0400
@@ -24,5 +24,7 @@ DEFINE(UM_ELF_CLASS, ELF_CLASS);
DEFINE(UM_ELFCLASS32, ELFCLASS32);
DEFINE(UM_ELFCLASS64, ELFCLASS64);

+DEFINE(UM_NR_CPUS, NR_CPUS);
+
/* For crypto assembler code. */
DEFINE(crypto_tfm_ctx_offset, offsetof(struct crypto_tfm, __crt_ctx));
Index: linux-2.6.21-mm/arch/um/os-Linux/skas/trap.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/os-Linux/skas/trap.c 2007-04-02 12:19:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/os-Linux/skas/trap.c 2007-04-02 12:19:07.000000000 -0400
@@ -15,6 +15,8 @@
#include "sysdep/ptrace_user.h"
#include "os.h"

+static union uml_pt_regs ksig_regs[UM_NR_CPUS];
+
void sig_handler_common_skas(int sig, void *sc_ptr)
{
struct sigcontext *sc = sc_ptr;
@@ -27,10 +29,19 @@ void sig_handler_common_skas(int sig, vo
* the process will die.
* XXX Figure out why this is better than SA_NODEFER
*/
- if(sig == SIGSEGV)
+ if(sig == SIGSEGV) {
change_sig(SIGSEGV, 1);
+ /* For segfaults, we want the data from the
+ * sigcontext. In this case, we don't want to mangle
+ * the process registers, so use a static set of
+ * registers. For other signals, the process
+ * registers are OK.
+ */
+ r = &ksig_regs[cpu()];
+ copy_sc(r, sc_ptr);
+ }
+ else r = TASK_REGS(get_current());

- r = TASK_REGS(get_current());
save_user = r->skas.is_user;
r->skas.is_user = 0;
if ( sig == SIGFPE || sig == SIGSEGV ||
Index: linux-2.6.21-mm/arch/um/sys-i386/signal.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/sys-i386/signal.c 2007-04-02 12:19:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/sys-i386/signal.c 2007-04-02 12:19:07.000000000 -0400
@@ -18,6 +18,28 @@

#include "skas.h"

+void copy_sc(union uml_pt_regs *regs, void *from)
+{
+ struct sigcontext *sc = from;
+
+ REGS_GS(regs->skas.regs) = sc->gs;
+ REGS_FS(regs->skas.regs) = sc->fs;
+ REGS_ES(regs->skas.regs) = sc->es;
+ REGS_DS(regs->skas.regs) = sc->ds;
+ REGS_EDI(regs->skas.regs) = sc->edi;
+ REGS_ESI(regs->skas.regs) = sc->esi;
+ REGS_EBP(regs->skas.regs) = sc->ebp;
+ REGS_SP(regs->skas.regs) = sc->esp;
+ REGS_EBX(regs->skas.regs) = sc->ebx;
+ REGS_EDX(regs->skas.regs) = sc->edx;
+ REGS_ECX(regs->skas.regs) = sc->ecx;
+ REGS_EAX(regs->skas.regs) = sc->eax;
+ REGS_IP(regs->skas.regs) = sc->eip;
+ REGS_CS(regs->skas.regs) = sc->cs;
+ REGS_EFLAGS(regs->skas.regs) = sc->eflags;
+ REGS_SS(regs->skas.regs) = sc->ss;
+}
+
static int copy_sc_from_user_skas(struct pt_regs *regs,
struct sigcontext __user *from)
{
@@ -30,25 +52,10 @@ static int copy_sc_from_user_skas(struct
if(err)
return err;

- REGS_GS(regs->regs.skas.regs) = sc.gs;
- REGS_FS(regs->regs.skas.regs) = sc.fs;
- REGS_ES(regs->regs.skas.regs) = sc.es;
- REGS_DS(regs->regs.skas.regs) = sc.ds;
- REGS_EDI(regs->regs.skas.regs) = sc.edi;
- REGS_ESI(regs->regs.skas.regs) = sc.esi;
- REGS_EBP(regs->regs.skas.regs) = sc.ebp;
- REGS_SP(regs->regs.skas.regs) = sc.esp;
- REGS_EBX(regs->regs.skas.regs) = sc.ebx;
- REGS_EDX(regs->regs.skas.regs) = sc.edx;
- REGS_ECX(regs->regs.skas.regs) = sc.ecx;
- REGS_EAX(regs->regs.skas.regs) = sc.eax;
- REGS_IP(regs->regs.skas.regs) = sc.eip;
- REGS_CS(regs->regs.skas.regs) = sc.cs;
- REGS_EFLAGS(regs->regs.skas.regs) = sc.eflags;
- REGS_SS(regs->regs.skas.regs) = sc.ss;
+ copy_sc(&regs->regs, &sc);

err = restore_fp_registers(userspace_pid[0], fpregs);
- if(err < 0){
+ if(err < 0) {
printk("copy_sc_from_user_skas - PTRACE_SETFPREGS failed, "
"errno = %d\n", -err);
return err;
Index: linux-2.6.21-mm/arch/um/sys-x86_64/signal.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/sys-x86_64/signal.c 2007-04-02 12:19:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/sys-x86_64/signal.c 2007-04-02 12:19:07.000000000 -0400
@@ -20,6 +20,36 @@

#include "skas.h"

+void copy_sc(union uml_pt_regs *regs, void *from)
+{
+ struct sigcontext *sc = from;
+
+#define GETREG(regs, regno, sc, regname) \
+ (regs)->skas.regs[(regno) / sizeof(unsigned long)] = (sc)->regname
+
+ GETREG(regs, R8, sc, r8);
+ GETREG(regs, R9, sc, r9);
+ GETREG(regs, R10, sc, r10);
+ GETREG(regs, R11, sc, r11);
+ GETREG(regs, R12, sc, r12);
+ GETREG(regs, R13, sc, r13);
+ GETREG(regs, R14, sc, r14);
+ GETREG(regs, R15, sc, r15);
+ GETREG(regs, RDI, sc, rdi);
+ GETREG(regs, RSI, sc, rsi);
+ GETREG(regs, RBP, sc, rbp);
+ GETREG(regs, RBX, sc, rbx);
+ GETREG(regs, RDX, sc, rdx);
+ GETREG(regs, RAX, sc, rax);
+ GETREG(regs, RCX, sc, rcx);
+ GETREG(regs, RSP, sc, rsp);
+ GETREG(regs, RIP, sc, rip);
+ GETREG(regs, EFLAGS, sc, eflags);
+ GETREG(regs, CS, sc, cs);
+
+#undef GETREG
+}
+
static int copy_sc_from_user_skas(struct pt_regs *regs,
struct sigcontext __user *from)
{
-
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