Commit 2c27d4a4 authored by Rohan McLure's avatar Rohan McLure Committed by Michael Ellerman
Browse files

powerpc: Save caller r3 prior to system_call_exception 



This reverts commit 8875f47b ("powerpc/syscall: Save r3 in regs->orig_r3
").

Save caller's original r3 state to the kernel stackframe before entering
system_call_exception. This allows for user registers to be cleared by
the time system_call_exception is entered, reducing the influence of
user registers on speculation within the kernel.

Prior to this commit, orig_r3 was saved at the beginning of
system_call_exception. Instead, save orig_r3 while the user value is
still live in r3.

Also replicate this early save in 32-bit. A similar save was removed in
commit 6f76a011 ("powerpc/syscall: implement system call entry/exit
logic in C for PPC32") when 32-bit adopted system_call_exception. Revert
its removal of orig_r3 saves.

Signed-off-by: default avatarRohan McLure <rmclure@linux.ibm.com>
Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220921065605.1051927-3-rmclure@linux.ibm.com
parent 5ba6c9a9

arch/powerpc/kernel/entry_32.S

+1 −0
Original line number Diff line number Diff line
@@ -101,6 +101,7 @@ __kuep_unlock: 


	.globl	transfer_to_syscall

transfer_to_syscall:

	stw	r3, ORIG_GPR3(r1)

	stw	r11, GPR1(r1)

	stw	r11, 0(r1)

	mflr	r12

arch/powerpc/kernel/interrupt_64.S

+2 −0
Original line number Diff line number Diff line
@@ -81,6 +81,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name) 
	li	r11,\trapnr

	std	r11,_TRAP(r1)

	std	r12,_CCR(r1)

	std	r3,ORIG_GPR3(r1)

	addi	r10,r1,STACK_FRAME_OVERHEAD

	ld	r11,exception_marker@toc(r2)

	std	r11,-16(r10)		/* "regshere" marker */
@@ -265,6 +266,7 @@ END_BTB_FLUSH_SECTION 
	std	r10,_LINK(r1)

	std	r11,_TRAP(r1)

	std	r12,_CCR(r1)

	std	r3,ORIG_GPR3(r1)

	addi	r10,r1,STACK_FRAME_OVERHEAD

	ld	r11,exception_marker@toc(r2)

	std	r11,-16(r10)		/* "regshere" marker */

arch/powerpc/kernel/syscall.c

+0 −1
Original line number Diff line number Diff line
@@ -25,7 +25,6 @@ notrace long system_call_exception(long r3, long r4, long r5, 
	kuap_lock();



	add_random_kstack_offset();

	regs->orig_gpr3 = r3;



	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))

		BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);