* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* This automated bisection report was sent to you on the basis  *
* that you may be involved with the breaking commit it has      *
* found.  No manual investigation has been done to verify it,   *
* and the root cause of the problem may be somewhere else.      *
*                                                               *
* If you do send a fix, please include this trailer:            *
*   Reported-by: "kernelci.org bot" [off-list ref]          *
*                                                               *
* Hope this helps!                                              *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

next/master bisection: baseline.login on ox820-cloudengines-pogoplug-series-3

Summary:
  Start:      90cc8cf2d1ab Add linux-next specific files for 20201217
  Plain log:  https://storage.kernelci.org/next/master/next-20201217/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/baseline-ox820-cloudengines-pogoplug-series-3.txt
  HTML log:   https://storage.kernelci.org/next/master/next-20201217/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/baseline-ox820-cloudengines-pogoplug-series-3.html
  Result:     f77ac2e378be ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode

Checks:
  revert:     PASS
  verify:     PASS

Parameters:
  Tree:       next
  URL:        https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
  Branch:     master
  Target:     ox820-cloudengines-pogoplug-series-3
  CPU arch:   arm
  Lab:        lab-baylibre
  Compiler:   gcc-8
  Config:     oxnas_v6_defconfig
  Test case:  baseline.login

Breaking commit found:

-------------------------------------------------------------------------------
commit f77ac2e378be9dd61eb88728f0840642f045d9d1
Author: Ard Biesheuvel [off-list ref]
Date:   Thu Nov 19 18:09:16 2020 +0100

    ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
    
    There are a couple of problems with the exception entry code that deals
    with FP exceptions (which are reported as UND exceptions) when building
    the kernel in Thumb2 mode:
    - the conditional branch to vfp_kmode_exception in vfp_support_entry()
      may be out of range for its target, depending on how the linker decides
      to arrange the sections;
    - when the UND exception is taken in kernel mode, the emulation handling
      logic is entered via the 'call_fpe' label, which means we end up using
      the wrong value/mask pairs to match and detect the NEON opcodes.
    
    Since UND exceptions in kernel mode are unlikely to occur on a hot path
    (as opposed to the user mode version which is invoked for VFP support
    code and lazy restore), we can use the existing undef hook machinery for
    any kernel mode instruction emulation that is needed, including calling
    the existing vfp_kmode_exception() routine for unexpected cases. So drop
    the call to call_fpe, and instead, install an undef hook that will get
    called for NEON and VFP instructions that trigger an UND exception in
    kernel mode.
    
    While at it, make sure that the PC correction is accurate for the
    execution mode where the exception was taken, by checking the PSR
    Thumb bit.
    
    Cc: Dmitry Osipenko [off-list ref]
    Cc: Kees Cook [off-list ref]
    Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections")
    Signed-off-by: Ard Biesheuvel [off-list ref]
    Reviewed-by: Linus Walleij [off-list ref]
    Reviewed-by: Nick Desaulniers [off-list ref]
    Signed-off-by: Russell King [off-list ref]

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index c4220f51fcf3..0ea8529a4872 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S

@@ -252,31 +252,10 @@ __und_svc:
 #else
 	svc_entry
 #endif
-	@
-	@ call emulation code, which returns using r9 if it has emulated
-	@ the instruction, or the more conventional lr if we are to treat
-	@ this as a real undefined instruction
-	@
-	@  r0 - instruction
-	@
-#ifndef CONFIG_THUMB2_KERNEL
-	ldr	r0, [r4, #-4]
-#else
-	mov	r1, #2
-	ldrh	r0, [r4, #-2]			@ Thumb instruction at LR - 2
-	cmp	r0, #0xe800			@ 32-bit instruction if xx >= 0
-	blo	__und_svc_fault
-	ldrh	r9, [r4]			@ bottom 16 bits
-	add	r4, r4, #2
-	str	r4, [sp, #S_PC]
-	orr	r0, r9, r0, lsl #16
-#endif
-	badr	r9, __und_svc_finish
-	mov	r2, r4
-	bl	call_fpe
 
 	mov	r1, #4				@ PC correction to apply
-__und_svc_fault:
+ THUMB(	tst	r5, #PSR_T_BIT		)	@ exception taken in Thumb mode?
+ THUMB(	movne	r1, #2			)	@ if so, fix up PC correction
 	mov	r0, sp				@ struct pt_regs *regs
 	bl	__und_fault
 

diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index 4fcff9f59947..d5837bf05a9a 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S

@@ -79,11 +79,6 @@ ENTRY(vfp_support_entry)
 	DBGSTR3	"instr %08x pc %08x state %p", r0, r2, r10
 
 	.fpu	vfpv2
-	ldr	r3, [sp, #S_PSR]	@ Neither lazy restore nor FP exceptions
-	and	r3, r3, #MODE_MASK	@ are supported in kernel mode
-	teq	r3, #USR_MODE
-	bne	vfp_kmode_exception	@ Returns through lr
-
 	VFPFMRX	r1, FPEXC		@ Is the VFP enabled?
 	DBGSTR1	"fpexc %08x", r1
 	tst	r1, #FPEXC_EN

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 8c9e7f9f0277..c3b6451c18bd 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c

@@ -23,6 +23,7 @@
 #include <asm/cputype.h>
 #include <asm/system_info.h>
 #include <asm/thread_notify.h>
+#include <asm/traps.h>
 #include <asm/vfp.h>
 
 #include "vfpinstr.h"

@@ -642,7 +643,9 @@ static int vfp_starting_cpu(unsigned int unused)
 	return 0;
 }
 
-void vfp_kmode_exception(void)
+#ifdef CONFIG_KERNEL_MODE_NEON
+
+static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)
 {
 	/*
 	 * If we reach this point, a floating point exception has been raised

@@ -660,9 +663,51 @@ void vfp_kmode_exception(void)
 		pr_crit("BUG: unsupported FP instruction in kernel mode\n");
 	else
 		pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n");
+	pr_crit("FPEXC == 0x%08x\n", fmrx(FPEXC));
+	return 1;
 }
 
-#ifdef CONFIG_KERNEL_MODE_NEON
+static struct undef_hook vfp_kmode_exception_hook[] = {{
+	.instr_mask	= 0xfe000000,
+	.instr_val	= 0xf2000000,
+	.cpsr_mask	= MODE_MASK | PSR_T_BIT,
+	.cpsr_val	= SVC_MODE,
+	.fn		= vfp_kmode_exception,
+}, {
+	.instr_mask	= 0xff100000,
+	.instr_val	= 0xf4000000,
+	.cpsr_mask	= MODE_MASK | PSR_T_BIT,
+	.cpsr_val	= SVC_MODE,
+	.fn		= vfp_kmode_exception,
+}, {
+	.instr_mask	= 0xef000000,
+	.instr_val	= 0xef000000,
+	.cpsr_mask	= MODE_MASK | PSR_T_BIT,
+	.cpsr_val	= SVC_MODE | PSR_T_BIT,
+	.fn		= vfp_kmode_exception,
+}, {
+	.instr_mask	= 0xff100000,
+	.instr_val	= 0xf9000000,
+	.cpsr_mask	= MODE_MASK | PSR_T_BIT,
+	.cpsr_val	= SVC_MODE | PSR_T_BIT,
+	.fn		= vfp_kmode_exception,
+}, {
+	.instr_mask	= 0x0c000e00,
+	.instr_val	= 0x0c000a00,
+	.cpsr_mask	= MODE_MASK,
+	.cpsr_val	= SVC_MODE,
+	.fn		= vfp_kmode_exception,
+}};
+
+static int __init vfp_kmode_exception_hook_init(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(vfp_kmode_exception_hook); i++)
+		register_undef_hook(&vfp_kmode_exception_hook[i]);
+	return 0;
+}
+core_initcall(vfp_kmode_exception_hook_init);
 
 /*
  * Kernel-side NEON support functions
-------------------------------------------------------------------------------

Git bisection log:

-------------------------------------------------------------------------------
git bisect start
# good: [31f6551ad75608d9c71fd4d3548c33f1abc52093] cifs: handle "guest" mount parameter
git bisect good 31f6551ad75608d9c71fd4d3548c33f1abc52093
# bad: [90cc8cf2d1ab87d708ebc311ac104ccbbefad9fc] Add linux-next specific files for 20201217
git bisect bad 90cc8cf2d1ab87d708ebc311ac104ccbbefad9fc
# good: [3db1a3fa98808aa90f95ec3e0fa2fc7abf28f5c9] Merge tag 'staging-5.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
git bisect good 3db1a3fa98808aa90f95ec3e0fa2fc7abf28f5c9
# bad: [4538b80cd2885c885e3bf06e5103bc0f214c11ee] Merge remote-tracking branch 'arm-soc/for-next'
git bisect bad 4538b80cd2885c885e3bf06e5103bc0f214c11ee
# good: [5ee863bec794f30bdf7fdf57ce0d9f579b0d1aa3] Merge branch 'parisc-5.11-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
git bisect good 5ee863bec794f30bdf7fdf57ce0d9f579b0d1aa3
# good: [fb10b701887b9fce88aacc06ca4b6c9160ca7a66] Merge branch 'arm/dt' into for-next
git bisect good fb10b701887b9fce88aacc06ca4b6c9160ca7a66
# good: [821a8a63a6b55ee5325e07bf5ab7d7a1752009d1] Merge remote-tracking branch 'asm-generic/master'
git bisect good 821a8a63a6b55ee5325e07bf5ab7d7a1752009d1
# good: [7debceff46eef5350bf2b62494c7772f78b22257] Merge branch 'arm/dt' into for-next
git bisect good 7debceff46eef5350bf2b62494c7772f78b22257
# bad: [b383a1412e0df59c556abb93c1fa2399e91b6102] Merge remote-tracking branch 'arm64/for-next/core'
git bisect bad b383a1412e0df59c556abb93c1fa2399e91b6102
# good: [113eb4ce4fc33ef3deda1431497811d43342c0cc] Merge branch 'for-next/iommu/vt-d' into for-next/iommu/core
git bisect good 113eb4ce4fc33ef3deda1431497811d43342c0cc
# skip: [eb86b15a2c53e2263b7cbad00a0100c8451989dc] Merge branches 'fixes' and 'misc' into for-next
git bisect skip eb86b15a2c53e2263b7cbad00a0100c8451989dc
# skip: [2a50d6b9cfe96ef5d39b9c3497dcc83a907d00cd] ARM: 9033/1: arm/smp: Drop the macro S(x,s)
git bisect skip 2a50d6b9cfe96ef5d39b9c3497dcc83a907d00cd
# good: [421015713b306e47af95d4d61cdfbd96d462e4cb] ARM: 9017/2: Enable KASan for ARM
git bisect good 421015713b306e47af95d4d61cdfbd96d462e4cb
# good: [2c736bb4087f2cb949cbbaf4148733131b8466dc] Merge tag 'arm-adrl-replacement-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux into devel-stable
git bisect good 2c736bb4087f2cb949cbbaf4148733131b8466dc
# skip: [3597a10e4c444f3d4d6a64bdc98e4585a99301b9] ARM: 9036/1: uncompress: Fix dbgadtb size parameter name
git bisect skip 3597a10e4c444f3d4d6a64bdc98e4585a99301b9
# skip: [1205285c7a71c3b7a879e31ec477639f2dac22b1] ARM: 9027/1: head.S: explicitly map DT even if it lives in the first physical section
git bisect skip 1205285c7a71c3b7a879e31ec477639f2dac22b1
# good: [71fe89ceb55bc0a85121b757cc8d3fb6ff457263] dma-iommu: remove __iommu_dma_mmap
git bisect good 71fe89ceb55bc0a85121b757cc8d3fb6ff457263
# skip: [17fb1a208129e3472ec45be08cbe39601a407e2c] ARM: 9031/1: hyp-stub: remove unused .L__boot_cpu_mode_offset symbol
git bisect skip 17fb1a208129e3472ec45be08cbe39601a407e2c
# good: [95d1718c961e49cfa02995ce1587a22cd7e2fbf5] Merge remote-tracking branch 'arm64/for-next/iommu/core' into for-next/core
git bisect good 95d1718c961e49cfa02995ce1587a22cd7e2fbf5
# skip: [0fe88ade3f937d6efc276901a56be6575a5a2171] ARM: 9032/1: arm/mm: Convert PUD level pgtable helper macros into functions
git bisect skip 0fe88ade3f937d6efc276901a56be6575a5a2171
# good: [730b5764ea8526e48bdb85a24ed96d62de435940] ARM: 9024/1: Drop useless cast of "u64" to "long long"
git bisect good 730b5764ea8526e48bdb85a24ed96d62de435940
# good: [4d576cab16f57e1f87978f6997a725179398341e] ARM: 9028/1: disable KASAN in call stack capturing routines
git bisect good 4d576cab16f57e1f87978f6997a725179398341e
# skip: [3bdf1a7503d61d2241f93f36e9c0d8a0d444bc5c] ARM: 9037/1: uncompress: Add OF_DT_MAGIC macro
git bisect skip 3bdf1a7503d61d2241f93f36e9c0d8a0d444bc5c
# bad: [f77ac2e378be9dd61eb88728f0840642f045d9d1] ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
git bisect bad f77ac2e378be9dd61eb88728f0840642f045d9d1
# good: [3c9f5708b7aed6a963e2aefccbd1854802de163e] ARM: 9029/1: Make iwmmxt.S support Clang's integrated assembler
git bisect good 3c9f5708b7aed6a963e2aefccbd1854802de163e
# first bad commit: [f77ac2e378be9dd61eb88728f0840642f045d9d1] ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
-------------------------------------------------------------------------------


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#4773): https://groups.io/g/kernelci-results/message/4773
Mute This Topic: https://groups.io/mt/79040317/924702
Group Owner: kernelci-results+owner@groups.io
Unsubscribe: https://groups.io/g/kernelci-results/unsub [guillaume.tucker@collabora.com]
-=-=-=-=-=-=-=-=-=-=-=-