From: Raoni Fassina Firmino raoni@linux.ibm.com
commit 24321ac668e452a4942598533d267805f291fdc9 upstream.
Commit 0138ba5783ae ("powerpc/64/signal: Balance return predictor stack in signal trampoline") changed __kernel_sigtramp_rt64() VDSO and trampoline code, and introduced a regression in the way glibc's backtrace()[1] detects the signal-handler stack frame. Apart from the practical implications, __kernel_sigtramp_rt64() was a VDSO function with the semantics that it is a function you can call from userspace to end a signal handling. Now this semantics are no longer valid.
I believe the aforementioned change affects all releases since 5.9.
This patch tries to fix both the semantics and practical aspect of __kernel_sigtramp_rt64() returning it to the previous code, whilst keeping the intended behaviour of 0138ba5783ae by adding a new symbol to serve as the jump target from the kernel to the trampoline. Now the trampoline has two parts, a new entry point and the old return point.
[1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-January/223194.html
Fixes: 0138ba5783ae ("powerpc/64/signal: Balance return predictor stack in signal trampoline") Cc: stable@vger.kernel.org # v5.9+ Signed-off-by: Raoni Fassina Firmino raoni@linux.ibm.com Acked-by: Nicholas Piggin npiggin@gmail.com [mpe: Minor tweaks to change log formatting, add stable tag] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20210201200505.iz46ubcizipnkcxe@work-tp Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/vdso.c | 2 +- arch/powerpc/kernel/vdso64/sigtramp.S | 11 ++++++++++- arch/powerpc/kernel/vdso64/vdso64.lds.S | 1 + 3 files changed, 12 insertions(+), 2 deletions(-)
--- a/arch/powerpc/kernel/vdso.c +++ b/arch/powerpc/kernel/vdso.c @@ -475,7 +475,7 @@ static __init void vdso_setup_trampoline */
#ifdef CONFIG_PPC64 - vdso64_rt_sigtramp = find_function64(v64, "__kernel_sigtramp_rt64"); + vdso64_rt_sigtramp = find_function64(v64, "__kernel_start_sigtramp_rt64"); #endif vdso32_sigtramp = find_function32(v32, "__kernel_sigtramp32"); vdso32_rt_sigtramp = find_function32(v32, "__kernel_sigtramp_rt32"); --- a/arch/powerpc/kernel/vdso64/sigtramp.S +++ b/arch/powerpc/kernel/vdso64/sigtramp.S @@ -15,11 +15,20 @@
.text
+/* + * __kernel_start_sigtramp_rt64 and __kernel_sigtramp_rt64 together + * are one function split in two parts. The kernel jumps to the former + * and the signal handler indirectly (by blr) returns to the latter. + * __kernel_sigtramp_rt64 needs to point to the return address so + * glibc can correctly identify the trampoline stack frame. + */ .balign 8 .balign IFETCH_ALIGN_BYTES -V_FUNCTION_BEGIN(__kernel_sigtramp_rt64) +V_FUNCTION_BEGIN(__kernel_start_sigtramp_rt64) .Lsigrt_start: bctrl /* call the handler */ +V_FUNCTION_END(__kernel_start_sigtramp_rt64) +V_FUNCTION_BEGIN(__kernel_sigtramp_rt64) addi r1, r1, __SIGNAL_FRAMESIZE li r0,__NR_rt_sigreturn sc --- a/arch/powerpc/kernel/vdso64/vdso64.lds.S +++ b/arch/powerpc/kernel/vdso64/vdso64.lds.S @@ -150,6 +150,7 @@ VERSION __kernel_get_tbfreq; __kernel_sync_dicache; __kernel_sync_dicache_p5; + __kernel_start_sigtramp_rt64; __kernel_sigtramp_rt64; __kernel_getcpu; __kernel_time;