Commit 41213bf2 authored by Deepak Gupta's avatar Deepak Gupta Committed by Paul Walmsley
Browse files

riscv: enable kernel access to shadow stack memory via the FWFT SBI call 



The kernel has to perform shadow stack operations on the user shadow stack.
During signal delivery and sigreturn, the shadow stack token must be
created and validated respectively. Thus shadow stack access for the kernel
must be enabled.

In the future, when kernel shadow stacks are enabled, they must be
enabled as early as possible for better coverage and to prevent any
imbalance between the regular stack and the shadow stack. After
'relocate_enable_mmu' has completed, this is the earliest that it can
be enabled.

Reviewed-by: default avatarZong Li <zong.li@sifive.com>
Signed-off-by: default avatarDeepak Gupta <debug@rivosinc.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de> # QEMU, custom CVA6
Tested-by: default avatarValentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-22-b55691eacf4f@rivosinc.com


[pjw@kernel.org: updated to apply; cleaned up commit message]
Signed-off-by: default avatarPaul Walmsley <pjw@kernel.org>
parent c9b859c4

arch/riscv/kernel/asm-offsets.c

+6 −0
Original line number Diff line number Diff line
@@ -533,4 +533,10 @@ void asm_offsets(void) 
	DEFINE(FREGS_A6,	    offsetof(struct __arch_ftrace_regs, a6));

	DEFINE(FREGS_A7,	    offsetof(struct __arch_ftrace_regs, a7));

#endif

#ifdef CONFIG_RISCV_SBI

	DEFINE(SBI_EXT_FWFT, SBI_EXT_FWFT);

	DEFINE(SBI_EXT_FWFT_SET, SBI_EXT_FWFT_SET);

	DEFINE(SBI_FWFT_SHADOW_STACK, SBI_FWFT_SHADOW_STACK);

	DEFINE(SBI_FWFT_SET_FLAG_LOCK, SBI_FWFT_SET_FLAG_LOCK);

#endif

}

arch/riscv/kernel/head.S

+27 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <asm/image.h>

#include <asm/scs.h>

#include <asm/xip_fixup.h>

#include <asm/usercfi.h>

#include "efi-header.S"



__HEAD
@@ -170,6 +171,19 @@ secondary_start_sbi: 
	call relocate_enable_mmu

#endif

	call .Lsetup_trap_vector

#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)

	li a7, SBI_EXT_FWFT

	li a6, SBI_EXT_FWFT_SET

	li a0, SBI_FWFT_SHADOW_STACK

	li a1, 1 /* enable supervisor to access shadow stack access */

	li a2, SBI_FWFT_SET_FLAG_LOCK

	ecall

	beqz a0, 1f

	la a1, riscv_nousercfi

	li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI

	REG_S a0, (a1)

1:

#endif

	scs_load_current

	call smp_callin

#endif /* CONFIG_SMP */
@@ -330,6 +344,19 @@ SYM_CODE_START(_start_kernel) 
	la tp, init_task

	la sp, init_thread_union + THREAD_SIZE

	addi sp, sp, -PT_SIZE_ON_STACK

#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)

	li a7, SBI_EXT_FWFT

	li a6, SBI_EXT_FWFT_SET

	li a0, SBI_FWFT_SHADOW_STACK

	li a1, 1 /* enable supervisor to access shadow stack access */

	li a2, SBI_FWFT_SET_FLAG_LOCK

	ecall

	beqz a0, 1f

	la a1, riscv_nousercfi

	li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI

	REG_S a0, (a1)

1:

#endif

	scs_load_current



#ifdef CONFIG_KASAN