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arm64: entry: Simplify tramp_alias macro and tramp_exit routine

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The tramp_alias macro constructs the virtual alias of a symbol in the
trampoline text mapping, based on its kernel text address, and does so
in a way that is more convoluted than necessary. So let's simplify that.

Also, now that the address of the vector table is kept in a per-CPU
variable, there is no need to defer the load and the assignment of
VBAR_EL1 to tramp_exit(). This means we can use a PC-relative reference
to the per-CPU variable instead of storing its absolute address in a
global variable in the trampoline rodata.

And given that tramp_alias no longer needs a temp register, this means
we can restore X30 earlier as well, and only leave X29 for tramp_exit()
to restore.

While at it, give some related symbols static linkage, considering that
they are only referenced from the object file that defines them.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230418143604.1176437-3-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel 2023-04-18 16:36:04 +02:00 committed by Catalin Marinas
parent 0936243cab
commit 211ceca377
1 changed files with 20 additions and 27 deletions
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47
arch/arm64/kernel/entry.S
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@ -101,12 +101,11 @@
.org .Lventry_start\@ + 128 // Did we overflow the ventry slot?
.endm
.macro tramp_alias, dst, sym, tmp
mov_q \dst, TRAMP_VALIAS
adr_l \tmp, \sym
add \dst, \dst, \tmp
adr_l \tmp, .entry.tramp.text
sub \dst, \dst, \tmp
.macro tramp_alias, dst, sym
.set .Lalias\@, TRAMP_VALIAS + \sym - .entry.tramp.text
movz \dst, :abs_g2_s:.Lalias\@
movk \dst, :abs_g1_nc:.Lalias\@
movk \dst, :abs_g0_nc:.Lalias\@
.endm
/*
@ -436,8 +435,13 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
alternative_else_nop_endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
msr far_el1, x29
tramp_alias x30, tramp_exit_native, x29
br x30
ldr_this_cpu x30, this_cpu_vector, x29
tramp_alias x29, tramp_exit
msr vbar_el1, x30 // install vector table
ldr lr, [sp, #S_LR] // restore x30
add sp, sp, #PT_REGS_SIZE // restore sp
br x29
#endif
.else
ldr lr, [sp, #S_LR]
@ -728,20 +732,6 @@ alternative_else_nop_endif
.org 1b + 128 // Did we overflow the ventry slot?
.endm
.macro tramp_exit, regsize = 64
tramp_data_read_var x30, this_cpu_vector
get_this_cpu_offset x29
ldr x30, [x30, x29]
msr vbar_el1, x30
ldr lr, [sp, #S_LR]
tramp_unmap_kernel x29
mrs x29, far_el1
add sp, sp, #PT_REGS_SIZE // restore sp
eret
sb
.endm
.macro generate_tramp_vector, kpti, bhb
.Lvector_start\@:
.space 0x400
@ -762,7 +752,7 @@ alternative_else_nop_endif
*/
.pushsection ".entry.tramp.text", "ax"
.align 11
SYM_CODE_START_NOALIGN(tramp_vectors)
SYM_CODE_START_LOCAL_NOALIGN(tramp_vectors)
#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_LOOP
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_FW
@ -771,9 +761,12 @@ SYM_CODE_START_NOALIGN(tramp_vectors)
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_NONE
SYM_CODE_END(tramp_vectors)
SYM_CODE_START(tramp_exit_native)
tramp_exit
SYM_CODE_END(tramp_exit_native)
SYM_CODE_START_LOCAL(tramp_exit)
tramp_unmap_kernel x29
mrs x29, far_el1 // restore x29
eret
sb
SYM_CODE_END(tramp_exit)
.popsection // .entry.tramp.text
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
@ -1067,7 +1060,7 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
alternative_else_nop_endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
tramp_alias dst=x5, sym=__sdei_asm_exit_trampoline, tmp=x3
tramp_alias dst=x5, sym=__sdei_asm_exit_trampoline
br x5
#endif
SYM_CODE_END(__sdei_asm_handler)