4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: LiuHailong <liu.hailong6@xxxxxxxxxx>
commit fd615f69a18a9d4aa5ef02a1dc83f319f75da8e7 upstream.
Debug interrupts can be taken during interrupt entry, since interrupt
entry does not automatically turn them off. The kernel will check
whether the faulting instruction is between [interrupt_base_book3e,
__end_interrupts], and if so clear MSR[DE] and return.
However, when the kernel is built with CONFIG_RELOCATABLE, it can't use
LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e) and
LOAD_REG_IMMEDIATE(r15,__end_interrupts), as they ignore relocation.
Thus, if the kernel is actually running at a different address than it
was built at, the address comparison will fail, and the exception entry
code will hang at kernel_dbg_exc.
r2(toc) is also not usable here, as r2 still holds data from the
interrupted context, so LOAD_REG_ADDR() doesn't work either. So we use
the *name@got* to get the EV of two labels directly.
Test programs test.c shows as follows:
int main(int argc, char *argv[])
{
if (access("/proc/sys/kernel/perf_event_paranoid", F_OK) == -1)
printf("Kernel doesn't have perf_event support\n");
}
Steps to reproduce the bug, for example:
1) ./gdb ./test
2) (gdb) b access
3) (gdb) r
4) (gdb) s
Signed-off-by: Liu Hailong <liu.hailong6@xxxxxxxxxx>
Signed-off-by: Jiang Xuexin <jiang.xuexin@xxxxxxxxxx>
Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
Reviewed-by: Liu Song <liu.song11@xxxxxxxxxx>
Reviewed-by: Huang Jian <huang.jian@xxxxxxxxxx>
[scottwood: cleaned up commit message, and specified bad behavior
as a hang rather than an oops to correspond to mainline kernel behavior]
Fixes: 1cb6e0649248 ("powerpc/book3e: support CONFIG_RELOCATABLE")
Signed-off-by: Scott Wood <oss@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kernel/exceptions-64e.S | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -735,8 +735,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
andis. r15,r14,(DBSR_IC|DBSR_BT)@h
beq+ 1f
+#ifdef CONFIG_RELOCATABLE
+ ld r15,PACATOC(r13)
+ ld r14,interrupt_base_book3e@got(r15)
+ ld r15,__end_interrupts@got(r15)
+#else
LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
LOAD_REG_IMMEDIATE(r15,__end_interrupts)
+#endif
cmpld cr0,r10,r14
cmpld cr1,r10,r15
blt+ cr0,1f
@@ -799,8 +805,14 @@ kernel_dbg_exc:
andis. r15,r14,(DBSR_IC|DBSR_BT)@h
beq+ 1f
+#ifdef CONFIG_RELOCATABLE
+ ld r15,PACATOC(r13)
+ ld r14,interrupt_base_book3e@got(r15)
+ ld r15,__end_interrupts@got(r15)
+#else
LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
LOAD_REG_IMMEDIATE(r15,__end_interrupts)
+#endif
cmpld cr0,r10,r14
cmpld cr1,r10,r15
blt+ cr0,1f