AUTONAK
On Mon, 30 May 2022 at 15:43, Sasha Levin sashal@kernel.org wrote:
From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit ad12c2f1587c6ec9b52ff226f438955bfae6ad89 ]
The assembler does not permit 'LDR PC, <sym>' when the symbol lives in a different section, which is why we have been relying on rather fragile open-coded arithmetic to load the address of the vector_swi routine into the program counter using a single LDR instruction in the SWI slot in the vector table. The literal was moved to a different section to in commit 19accfd373847 ("ARM: move vector stubs") to ensure that the vector stubs page does not need to be mapped readable for user space, which is the case for the vector page itself, as it carries the kuser helpers as well.
So the cross-section literal load is open-coded, and this relies on the address of vector_swi to be at the very start of the vector stubs page, and we won't notice if we got it wrong until booting the kernel and see it break. Fortunately, it was guaranteed to break, so this was fragile but not problematic.
Now that we have added two other variants of the vector table, we have 3 occurrences of the same trick, and so the size of our ISA/compiler/CPU validation space has tripled, in a way that may cause regressions to only be observed once booting the image in question on a CPU that exercises a particular vector table.
So let's switch to true cross section references, and let the linker fix them up like it fixes up all the other cross section references in the vector page.
Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Russell King (Oracle) rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org
arch/arm/kernel/entry-armv.S | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index 68261a83b7ad..01c5b3aee22f 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -1069,10 +1069,15 @@ ENDPROC(vector_bhb_bpiall_\name) .endm
.section .stubs, "ax", %progbits
@ This must be the first word
@ These need to remain at the start of the section so that@ they are in range of the 'SWI' entries in the vector tables@ located 4k down.+.L__vector_swi: .word vector_swi #ifdef CONFIG_HARDEN_BRANCH_HISTORY +.L__vector_bhb_loop8_swi: .word vector_bhb_loop8_swi +.L__vector_bhb_bpiall_swi: .word vector_bhb_bpiall_swi #endif
@@ -1215,10 +1220,11 @@ vector_addrexcptn: .globl vector_fiq
.section .vectors, "ax", %progbits-.L__vectors_start: W(b) vector_rst W(b) vector_und
W(ldr) pc, .L__vectors_start + 0x1000+ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_swi ) +THUMB( .reloc ., R_ARM_THM_PC12, .L__vector_swi )
W(ldr) pc, . W(b) vector_pabt W(b) vector_dabt W(b) vector_addrexcptn@@ -1227,10 +1233,11 @@ vector_addrexcptn:
#ifdef CONFIG_HARDEN_BRANCH_HISTORY .section .vectors.bhb.loop8, "ax", %progbits -.L__vectors_bhb_loop8_start: W(b) vector_rst W(b) vector_bhb_loop8_und
W(ldr) pc, .L__vectors_bhb_loop8_start + 0x1004+ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_bhb_loop8_swi ) +THUMB( .reloc ., R_ARM_THM_PC12, .L__vector_bhb_loop8_swi )
W(ldr) pc, . W(b) vector_bhb_loop8_pabt W(b) vector_bhb_loop8_dabt W(b) vector_addrexcptn@@ -1238,10 +1245,11 @@ vector_addrexcptn: W(b) vector_bhb_loop8_fiq
.section .vectors.bhb.bpiall, "ax", %progbits-.L__vectors_bhb_bpiall_start: W(b) vector_rst W(b) vector_bhb_bpiall_und
W(ldr) pc, .L__vectors_bhb_bpiall_start + 0x1008+ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_bhb_bpiall_swi ) +THUMB( .reloc ., R_ARM_THM_PC12, .L__vector_bhb_bpiall_swi )
W(ldr) pc, . W(b) vector_bhb_bpiall_pabt W(b) vector_bhb_bpiall_dabt W(b) vector_addrexcptn-- 2.35.1