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ARM: 9297/1: vfp: avoid unbalanced stack on 'success' return path

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Commit c76c6c4ecb ("ARM: 9294/2: vfp: Fix broken softirq handling
with instrumentation enabled") updated the VFP exception entry logic to
go via a C function, so that we get the compiler's version of
local_bh_disable(), which may be instrumented, and isn't generally
callable from assembler.

However, this assumes that passing an alternative 'success' return
address works in C as it does in asm, and this is only the case if the C
calls in question are tail calls, as otherwise, the stack will need some
unwinding as well.

I have already sent patches to the list that replace most of the asm
logic with C code, and so it is preferable to have a minimal fix that
addresses the issue and can be backported along with the commit that it

fixes to v6.3 from v6.4. Hopefully, we can land the C conversion for v6.5.

So instead of passing the 'success' return address as a function
argument, pass the stack address from where to pop it so that both LR
and SP have the expected value.

Fixes: c76c6c4ecb ("ARM: 9294/2: vfp: Fix broken softirq handling with ...")
Reported-by: syzbot+d4b00edc2d0c910d4bf4@syzkaller.appspotmail.com
Tested-by: syzbot+d4b00edc2d0c910d4bf4@syzkaller.appspotmail.com
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Ard Biesheuvel 2023-05-08 13:40:19 +01:00 committed by Russell King (Oracle)
parent 46dd6078db
commit 2b951b0efb
2 changed files with 9 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
arch/arm/vfp/entry.S
View File

@ -23,6 +23,9 @@
@
ENTRY(do_vfp)
mov r1, r10
mov r3, r9
b vfp_entry
str lr, [sp, #-8]!
add r3, sp, #4
str r9, [r3]
bl vfp_entry
ldr pc, [sp], #8
ENDPROC(do_vfp)

6
arch/arm/vfp/vfphw.S
View File

@ -172,13 +172,14 @@ vfp_hw_state_valid:
@ out before setting an FPEXC that
@ stops us reading stuff
VFPFMXR FPEXC, r1 @ Restore FPEXC last
mov sp, r3 @ we think we have handled things
pop {lr}
sub r2, r2, #4 @ Retry current instruction - if Thumb
str r2, [sp, #S_PC] @ mode it's two 16-bit instructions,
@ else it's one 32-bit instruction, so
@ always subtract 4 from the following
@ instruction address.
mov lr, r3 @ we think we have handled things
local_bh_enable_and_ret:
adr r0, .
mov r1, #SOFTIRQ_DISABLE_OFFSET
@ -209,8 +210,9 @@ skip:
process_exception:
DBGSTR "bounce"
mov sp, r3 @ setup for a return to the user code.
pop {lr}
mov r2, sp @ nothing stacked - regdump is at TOS
mov lr, r3 @ setup for a return to the user code.
@ Now call the C code to package up the bounce to the support code
@ r0 holds the trigger instruction