uml: kernel segfaults should dump proper registers

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@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/um/include/common-offsets.h b/arch/um/include/common-offsets.h
index 461175f8b1d9da4b4c14f21616ea4ec2016e1409..5593a802708321ac919247574bf16ec48856c246 100644 (file)
--- a/arch/um/include/common-offsets.h
+++ b/arch/um/include/common-offsets.h
@@ -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));

diff --git a/arch/um/include/kern_util.h b/arch/um/include/kern_util.h
index 092a2841556fd056a10eee5f15b2636edb407382..50a49691e0e62fd3666851de8b70c2b521d1074f 100644 (file)
--- a/arch/um/include/kern_util.h
+++ b/arch/um/include/kern_util.h
@@ -115,4 +115,6 @@ extern void time_init_kern(void);
 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

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index c3e62e634c0a7473388261b0ea3f11016e5eea62..0c467fa08870d49a39cecf34a751a98b8e646c67 100644 (file)
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -170,8 +170,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
                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, unsigned long ip, int is_user,
        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;

diff --git a/arch/um/os-Linux/skas/trap.c b/arch/um/os-Linux/skas/trap.c
index 6a20d08caf91bb45f3a8671b1262cdf416e1771d..5110eff51b90f968dfe31740183177943d38fe7c 100644 (file)
--- a/arch/um/os-Linux/skas/trap.c
+++ b/arch/um/os-Linux/skas/trap.c
@@ -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, void *sc_ptr)
         * 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 ||

diff --git a/arch/um/sys-i386/signal.c b/arch/um/sys-i386/signal.c
index 42ecf8e8ad080eeb9c3cb66b2a605a60042c77c1..1cbf95f6858ae2b0a97fcb7c87cd711338da1331 100644 (file)
--- a/arch/um/sys-i386/signal.c
+++ b/arch/um/sys-i386/signal.c
@@ -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 pt_regs *regs,
        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;

diff --git a/arch/um/sys-x86_64/signal.c b/arch/um/sys-x86_64/signal.c
index 068006213598b29473e311e7c8a4ee50712f0e41..fe8ec04d35bbbecc9b685702f69c44b6df4b6be0 100644 (file)
--- a/arch/um/sys-x86_64/signal.c
+++ b/arch/um/sys-x86_64/signal.c
@@ -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)
 {