This is a note to let you know that I've just added the patch titled
arm64: entry: Allow tramp_alias to access symbols after the 4K boundary
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-entry-allow-tramp_alias-to-access-symbols-afte.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e73cd5a4e733a19be287b78703dd41c44dde542f
Author: James Morse <james.morse@xxxxxxx>
Date: Tue Mar 15 18:24:02 2022 +0000
arm64: entry: Allow tramp_alias to access symbols after the 4K boundary
commit 6c5bf79b69f911560fbf82214c0971af6e58e682 upstream.
Systems using kpti enter and exit the kernel through a trampoline mapping
that is always mapped, even when the kernel is not. tramp_valias is a macro
to find the address of a symbol in the trampoline mapping.
Adding extra sets of vectors will expand the size of the entry.tramp.text
section to beyond 4K. tramp_valias will be unable to generate addresses
for symbols beyond 4K as it uses the 12 bit immediate of the add
instruction.
As there are now two registers available when tramp_alias is called,
use the extra register to avoid the 4K limit of the 12 bit immediate.
Reviewed-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 7822ecc0e165..3489edd57c51 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -124,9 +124,12 @@
.org .Lventry_start\@ + 128 // Did we overflow the ventry slot?
.endm
- .macro tramp_alias, dst, sym
+ .macro tramp_alias, dst, sym, tmp
mov_q \dst, TRAMP_VALIAS
- add \dst, \dst, #(\sym - .entry.tramp.text)
+ adr_l \tmp, \sym
+ add \dst, \dst, \tmp
+ adr_l \tmp, .entry.tramp.text
+ sub \dst, \dst, \tmp
.endm
// This macro corrupts x0-x3. It is the caller's duty
@@ -377,10 +380,10 @@ alternative_else_nop_endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
bne 5f
msr far_el1, x29
- tramp_alias x30, tramp_exit_native
+ tramp_alias x30, tramp_exit_native, x29
br x30
5:
- tramp_alias x30, tramp_exit_compat
+ tramp_alias x30, tramp_exit_compat, x29
br x30
#endif
.else
@@ -1362,7 +1365,7 @@ 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
+ tramp_alias dst=x5, sym=__sdei_asm_exit_trampoline, tmp=x3
br x5
#endif
ENDPROC(__sdei_asm_handler)
