From 1344a232016dbb0492be81f8517c4bf8fc1c6610 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Wed, 4 Nov 2020 22:17:42 +1100 Subject: powerpc: Use asm_goto_volatile for put_user() Andreas reported that commit ee0a49a6870e ("powerpc/uaccess: Switch __put_user_size_allowed() to __put_user_asm_goto()") broke CLONE_CHILD_SETTID. Further inspection showed that the put_user() in schedule_tail() was missing entirely, the store not emitted by the compiler. <.schedule_tail>: mflr r0 std r0,16(r1) stdu r1,-112(r1) bl <.finish_task_switch> ld r9,2496(r3) cmpdi cr7,r9,0 bne cr7,<.schedule_tail+0x60> ld r3,392(r13) ld r9,1392(r3) cmpdi cr7,r9,0 beq cr7,<.schedule_tail+0x3c> li r4,0 li r5,0 bl <.__task_pid_nr_ns> nop bl <.calculate_sigpending> nop addi r1,r1,112 ld r0,16(r1) mtlr r0 blr nop nop nop bl <.__balance_callback> b <.schedule_tail+0x1c> Notice there are no stores other than to the stack. There should be a stw in there for the store to current->set_child_tid. This is only seen with GCC 4.9 era compilers (tested with 4.9.3 and 4.9.4), and only when CONFIG_PPC_KUAP is disabled. When CONFIG_PPC_KUAP=y, the inline asm that's part of the isync() and mtspr() inlined via allow_user_access() seems to be enough to avoid the bug. We already have a macro to work around this (or a similar bug), called asm_volatile_goto which includes an empty asm block to tickle the compiler into generating the right code. So use that. With this applied the code generation looks more like it will work: <.schedule_tail>: mflr r0 std r31,-8(r1) std r0,16(r1) stdu r1,-144(r1) std r3,112(r1) bl <._mcount> nop ld r3,112(r1) bl <.finish_task_switch> ld r9,2624(r3) cmpdi cr7,r9,0 bne cr7,<.schedule_tail+0xa0> ld r3,2408(r13) ld r31,1856(r3) cmpdi cr7,r31,0 beq cr7,<.schedule_tail+0x80> li r4,0 li r5,0 bl <.__task_pid_nr_ns> nop li r9,-1 clrldi r9,r9,12 cmpld cr7,r31,r9 bgt cr7,<.schedule_tail+0x80> lis r9,16 rldicr r9,r9,32,31 subf r9,r31,r9 cmpldi cr7,r9,3 ble cr7,<.schedule_tail+0x80> li r9,0 stw r3,0(r31) <-- stw nop bl <.calculate_sigpending> nop addi r1,r1,144 ld r0,16(r1) ld r31,-8(r1) mtlr r0 blr nop bl <.__balance_callback> b <.schedule_tail+0x30> Fixes: ee0a49a6870e ("powerpc/uaccess: Switch __put_user_size_allowed() to __put_user_asm_goto()") Reported-by: Andreas Schwab Tested-by: Andreas Schwab Suggested-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201104111742.672142-1-mpe@ellerman.id.au --- arch/powerpc/include/asm/uaccess.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/powerpc/include/asm/uaccess.h') diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index ef5bbb705c08..501c9a79038c 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -178,7 +178,7 @@ do { \ * are no aliasing issues. */ #define __put_user_asm_goto(x, addr, label, op) \ - asm volatile goto( \ + asm_volatile_goto( \ "1: " op "%U1%X1 %0,%1 # put_user\n" \ EX_TABLE(1b, %l2) \ : \ @@ -191,7 +191,7 @@ do { \ __put_user_asm_goto(x, ptr, label, "std") #else /* __powerpc64__ */ #define __put_user_asm2_goto(x, addr, label) \ - asm volatile goto( \ + asm_volatile_goto( \ "1: stw%X1 %0, %1\n" \ "2: stw%X1 %L0, %L1\n" \ EX_TABLE(1b, %l2) \ -- cgit v1.2.3-59-g8ed1b