Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.11 129/197] powerpc/64e: Fix hang when debugging programs with relocated kernel | Date | Tue, 23 May 2017 22:08:10 +0200 |
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4.11-stable review patch. If anyone has any objections, please let me know.
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From: LiuHailong <liu.hailong6@zte.com.cn>
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@zte.com.cn> Signed-off-by: Jiang Xuexin <jiang.xuexin@zte.com.cn> Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn> Reviewed-by: Liu Song <liu.song11@zte.com.cn> Reviewed-by: Huang Jian <huang.jian@zte.com.cn> [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@buserror.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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
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