From 2b951b0efbaa6c805854b60c11f08811054d50cd Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Mon, 8 May 2023 13:40:19 +0100 Subject: ARM: 9297/1: vfp: avoid unbalanced stack on 'success' return path Commit c76c6c4ecbec0deb5 ("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: c76c6c4ecbec0deb5 ("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 Tested-by: Andrew Lunn Signed-off-by: Ard Biesheuvel Tested-by: Andre Przywara Signed-off-by: Russell King (Oracle) --- arch/arm/vfp/vfphw.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'arch/arm/vfp/vfphw.S') diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S index 4d8478264d82..a4610d0f3215 100644 --- a/arch/arm/vfp/vfphw.S +++ b/arch/arm/vfp/vfphw.S @@ -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 -- cgit