On Fri, 20 Dec 2019, Alexander Bluhm wrote:
> Can we use the regular trap panic for SMEP and SMAP? pageflttrap()
> returns 0 to print a nice reason in kerntrap(). Especially if ddb is
> disabled, additional information is printed.
>
> attempt to access user address 0xe27539f1000 in supervisor mode
> fatal page fault in supervisor mode
> trap type 6 code 3 rip ffffffff819c2665 cs 8 rflags 10202 cr2 e27539f1000 cpl
> 0 rsp ffff80001ffbfe28
> gsbase 0xffff80001fb63ff0 kgsbase 0x0
> panic: trap type 6, code=3, pc=ffffffff819c2665
...
> Index: arch/amd64/amd64/trap.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/arch/amd64/amd64/trap.c,v
> retrieving revision 1.77
> diff -u -p -r1.77 trap.c
> --- arch/amd64/amd64/trap.c 6 Sep 2019 12:22:01 -0000 1.77
> +++ arch/amd64/amd64/trap.c 19 Dec 2019 23:46:40 -0000
> @@ -163,14 +163,18 @@ pageflttrap(struct trapframe *frame, int
> extern struct vm_map *kernel_map;
>
> /* This will only trigger if SMEP is enabled */
> - if (cr2 <= VM_MAXUSER_ADDRESS && frame->tf_err & PGEX_I)
> - panic("attempt to execute user address %p "
> - "in supervisor mode", (void *)cr2);
> + if (cr2 <= VM_MAXUSER_ADDRESS && frame->tf_err & PGEX_I) {
> + printf("attempt to execute user address %p "
> + "in supervisor mode\n", (void *)cr2);
> + return 0;
> + }
> /* This will only trigger if SMAP is enabled */
> if (pcb->pcb_onfault == NULL && cr2 <= VM_MAXUSER_ADDRESS &&
> - frame->tf_err & PGEX_P)
> - panic("attempt to access user address %p "
> - "in supervisor mode", (void *)cr2);
> + frame->tf_err & PGEX_P) {
> + printf("attempt to access user address %p "
> + "in supervisor mode\n", (void *)cr2);
> + return 0;
> + }
>
> /*
> * It is only a kernel address space fault iff:
For this part, should we reuse the 'faultstr' logic seen later to set the
panic string and do something like, say...
Index: amd64/trap.c
===================================================================
RCS file: /data/src/openbsd/src/sys/arch/amd64/amd64/trap.c,v
retrieving revision 1.77
diff -u -p -r1.77 trap.c
--- amd64/trap.c 6 Sep 2019 12:22:01 -0000 1.77
+++ amd64/trap.c 20 Dec 2019 02:21:03 -0000
@@ -77,6 +77,7 @@
#include <sys/signal.h>
#include <sys/syscall.h>
#include <sys/syscall_mi.h>
+#include <sys/stdarg.h>
#include <uvm/uvm_extern.h>
@@ -132,6 +133,24 @@ static inline void verify_smap(const cha
static inline void debug_trap(struct trapframe *_frame, struct proc *_p,
long _type);
+static inline int
+fault(const char *format, ...)
+{
+ static char faultbuf[512];
+ va_list ap;
+
+ /*
+ * Save the fault info for DDB and retain the kernel lock to keep
+ * faultbuf from being overwritten by another CPU.
+ */
+ va_start(ap, format);
+ vsnprintf(faultbuf, sizeof faultbuf, format, ap);
+ va_end(ap);
+ printf("%s\n", faultbuf);
+ faultstr = faultbuf;
+ return 0;
+}
+
/*
* pageflttrap(frame, usermode): page fault handler
* Returns non-zero if the fault was handled (possibly by generating
@@ -164,12 +183,12 @@ pageflttrap(struct trapframe *frame, int
/* This will only trigger if SMEP is enabled */
if (cr2 <= VM_MAXUSER_ADDRESS && frame->tf_err & PGEX_I)
- panic("attempt to execute user address %p "
+ return fault("attempt to execute user address %p "
"in supervisor mode", (void *)cr2);
/* This will only trigger if SMAP is enabled */
if (pcb->pcb_onfault == NULL && cr2 <= VM_MAXUSER_ADDRESS &&
frame->tf_err & PGEX_P)
- panic("attempt to access user address %p "
+ return fault("attempt to access user address %p "
"in supervisor mode", (void *)cr2);
/*
@@ -211,18 +230,9 @@ pageflttrap(struct trapframe *frame, int
frame->tf_rip = (u_int64_t)pcb->pcb_onfault;
return 1;
} else {
- /*
- * Bad memory access in the kernel; save the fault
- * info for DDB and retain the kernel lock to keep
- * faultbuf from being overwritten by another CPU.
- */
- static char faultbuf[512];
- snprintf(faultbuf, sizeof faultbuf,
- "uvm_fault(%p, 0x%llx, 0, %d) -> %x",
+ /* bad memory access in the kernel */
+ return fault("uvm_fault(%p, 0x%llx, 0, %d) -> %x",
map, cr2, ftype, error);
- printf("%s\n", faultbuf);
- faultstr = faultbuf;
- return 0;
}
} else {
union sigval sv;
Philip
