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arm64: entry: Free up another register on kpti's tramp_exit path

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commit 03aff3a77a58b5b52a77e00537a42090ad57b80b upstream.

Kpti stashes x30 in far_el1 while it uses x30 for all its work.

Making the vectors a per-cpu data structure will require a second
register.

Allow tramp_exit two registers before it unmaps the kernel, by
leaving x30 on the stack, and stashing x29 in far_el1.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
James Morse 2022-03-15 18:24:00 +00:00 committed by Greg Kroah-Hartman
parent 3f95cc642c
commit 33397322d4
1 changed files with 12 additions and 6 deletions
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18
arch/arm64/kernel/entry.S
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@ -367,14 +367,16 @@ alternative_else_nop_endif
ldp x24, x25, [sp, #16 * 12]
ldp x26, x27, [sp, #16 * 13]
ldp x28, x29, [sp, #16 * 14]
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
.if \el == 0
alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
eret
alternative_else_nop_endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
bne 5f
msr far_el1, x30
msr far_el1, x29
tramp_alias x30, tramp_exit_native
br x30
5:
@ -382,6 +384,8 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
br x30
#endif
.else
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
eret
.endif
sb
@ -1092,10 +1096,12 @@ alternative_else_nop_endif
.macro tramp_exit, regsize = 64
adr x30, tramp_vectors
msr vbar_el1, x30
tramp_unmap_kernel x30
ldr lr, [sp, #S_LR]
tramp_unmap_kernel x29
.if \regsize == 64
mrs x30, far_el1
mrs x29, far_el1
.endif
add sp, sp, #S_FRAME_SIZE // restore sp
eret
sb
.endm