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Message-ID: <Yv3IRNKsTfF5IwvX@xpf.sh.intel.com>
Date: Thu, 18 Aug 2022 13:04:04 +0800
From: Pengfei Xu <pengfei.xu@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: "Yang, Weijiang" <weijiang.yang@...el.com>,
"Su, Heng" <heng.su@...el.com>, <linux-kernel@...r.kernel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>, <pbonzini@...hat.com>,
<x86@...nel.org>
Subject: Re: [PATCH] x86/kvm, objtool: Avoid fastop ENDBR from being sealed
Hi Peter,
On 2022-08-17 at 12:56:15 +0200, Peter Zijlstra wrote:
> On Tue, Aug 09, 2022 at 02:44:28AM +0000, Xu, Pengfei wrote:
> > Hi Peter,
> >
> > Greeting!
>
> You again forgot to Cc LKML and relevant people...
Ah, I will Cc LKML and relevant people if I report new issue next time.
I have tested your patch, and I could not rerproduce this issue
when starting the syzkaller test for more than 6 hours.
And I will test Josh Poimboeuf's patch, will update email if I find
some problem.
Thanks!
BR.
>
> > Platform: ADL-P (I tried that TGL-H could reproduce this issue also)
> > Kernel: 5.19 mainline kernel with kernel IBT enabled.
> >
> > Boot up ADL-P, and then run syzkaller fuzzing tests, syzkaller will start up guests(Guest kernel is 5.19 mainline also but doesn't enable kernel IBT) to do fuzzing tests.
> > After about 1 hour later, there was "traps: Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]" info generated.
> >
> > [ 5048.057266] traps: Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]
> > [ 5048.057440] ------------[ cut here ]------------
> > [ 5048.057457] kernel BUG at arch/x86/kernel/traps.c:253!
> > [ 5048.057482] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> > [ 5048.057908] <TASK>
> > [ 5048.057919] asm_exc_control_protection+0x2b/0x30
> > [ 5048.057940] RIP: 0010:andw_ax_dx+0x0/0x10 [kvm]
> > [ 5048.057999] Code: c3 cc cc cc cc 0f 1f 44 00 00 66 0f 1f 00 48 19 d0 c3 cc cc cc cc 0f 1f 40 00 f3 0f 1e fa 20 d0 c3 cc cc cc cc 0f 1f 44 00 00 <66> 0f 1f 00 66 21 d0 c3 cc cc cc cc 0f 1f 40 00 66 0f 1f 00 21 d0
> > ...
> > [ 5048.058209] ? andb_al_dl+0x10/0x10 [kvm]
> > [ 5048.058265] ? fastop+0x5d/0xa0 [kvm]
> > [ 5048.058320] x86_emulate_insn+0x822/0x1060 [kvm]
> > [ 5048.058376] x86_emulate_instruction+0x46f/0x750 [kvm]
> > [ 5048.058433] complete_emulated_mmio+0x216/0x2c0 [kvm]
> > [ 5048.058488] kvm_arch_vcpu_ioctl_run+0x604/0x650 [kvm]
> > [ 5048.058543] kvm_vcpu_ioctl+0x2f4/0x6b0 [kvm]
> > [ 5048.058590] ? wake_up_q+0xa0/0xa0
> > ...
> > [ 6324.778942] traps: Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]
> > ...
> > [ 8760.430810] traps: Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]
>
> Urgh, fastops again :/
>
> > Dmesg and all the ko files in "/lib/modules/5.19.0-m2/kernel/arch/x86" are in attached.
>
> From your kvm.ko:
>
> 00000000000376f0 <andw_ax_dx>:
> 376f0: f3 0f 1e fa endbr64
> 376f4: 66 21 d0 and %dx,%ax
> 376f7: e9 00 00 00 00 jmp 376fc <andw_ax_dx+0xc> 376f8: R_X86_64_PLT32 __x86_return_thunk-0x4
> 376fc: 0f 1f 40 00 nopl 0x0(%rax)
>
> However, the Code: thing above gives:
>
> 2a:* 66 0f 1f 00 nopw (%rax) <-- trapping instruction
> 2e: 66 21 d0 and %dx,%ax
> 31: c3 ret
> 32: cc int3
> 33: cc int3
> 34: cc int3
> 35: cc int3
> 36: 0f 1f 40 00 nopl 0x0(%rax)
>
> From that we can tell gen_endbr_poison() has been used to scribble the
> endbr -- so clearly objtool didn't manage to find code references here.
>
> And indeed, kvm.ko's .rela.ibt_endbr_seal section includes:
>
> 00000000000002c0 0000000100000002 R_X86_64_PC32 0000000000000000 .text + 376f0
>
> ---
> Subject: x86/kvm, objtool: Avoid fastop ENDBR from being sealed
>
> Xu reported a number of "Missing ENDBR" triggers for the KVM fastop
> emulation code. It turns out that because of how the fastops are set up,
> only the first of a series -- the 8 byte variants that overlap with the
> em_ symbols -- is found referenced.
>
> Specifically:
>
> .pushsection .text, "ax"
> .global em_and
> .align 16
> em_and:
> .align 16
> .type andb_al_dl, @function
> andb_al_dl:
> endbr64
> andb %dl, %al
> 11: jmp __x86_return_thunk
> .size andb_al_dl, .-andb_al_dl
> .align 16
> .type andw_ax_dx, @function
> andw_ax_dx:
> endbr64
> andw %dx, %ax
> 11: jmp __x86_return_thunk
> .size andw_ax_dx, .-andw_ax_dx
> .align 16
> .type andl_eax_edx, @function
> andl_eax_edx:
> endbr64
> andl %edx, %eax
> 11: jmp __x86_return_thunk
> .size andl_eax_edx, .-andl_eax_edx
> .align 16
> .type andq_rax_rdx, @function
> andq_rax_rdx:
> endbr64
> andq %rdx, %rax
> 11: jmp __x86_return_thunk
> .size andq_rax_rdx, .-andq_rax_rdx
> .popsection
>
> Only has the em_and symbol referenced, resulting in and{w,l,q}_* getting
> sealed.
>
> Add (yet another) annotation to inhibit objtool from sealing a specific
> ENDBR instance.
>
> Fixes: 6649fa876da4 ("x86/ibt,kvm: Add ENDBR to fastops")
> Reported-by: "Xu, Pengfei" <pengfei.xu@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> arch/x86/include/asm/ibt.h | 5 +++++
> arch/x86/kvm/emulate.c | 4 ++--
> include/linux/objtool.h | 6 ++++++
> tools/objtool/check.c | 44 ++++++++++++++++++++++++++++++++++++++------
> 4 files changed, 51 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h
> index 689880eca9ba..f32ba1c4e619 100644
> --- a/arch/x86/include/asm/ibt.h
> +++ b/arch/x86/include/asm/ibt.h
> @@ -29,6 +29,10 @@
> #define ASM_ENDBR "endbr32\n\t"
> #endif
>
> +#define ASM_ENDBR_NOSEAL \
> + ANNOTATE_NOSEAL \
> + ASM_ENDBR
> +
> #define __noendbr __attribute__((nocf_check))
>
> static inline __attribute_const__ u32 gen_endbr(void)
> @@ -84,6 +88,7 @@ extern __noendbr void ibt_restore(u64 save);
> #ifndef __ASSEMBLY__
>
> #define ASM_ENDBR
> +#define ASM_ENDBR_NOSEAL
>
> #define __noendbr
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b4eeb7c75dfa..d51ee8a3bcae 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -326,7 +326,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
> ".align " __stringify(FASTOP_SIZE) " \n\t" \
> ".type " name ", @function \n\t" \
> name ":\n\t" \
> - ASM_ENDBR
> + ASM_ENDBR_NOSEAL
>
> #define FOP_FUNC(name) \
> __FOP_FUNC(#name)
> @@ -461,7 +461,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
> ".align " __stringify(SETCC_ALIGN) " \n\t" \
> ".type " #op ", @function \n\t" \
> #op ": \n\t" \
> - ASM_ENDBR \
> + ASM_ENDBR_NOSEAL \
> #op " %al \n\t" \
> __FOP_RET(#op) \
> ".skip " __stringify(SETCC_ALIGN) " - (.-" #op "), 0xcc \n\t"
> diff --git a/include/linux/objtool.h b/include/linux/objtool.h
> index 62c54ffbeeaa..ad752f8b3b36 100644
> --- a/include/linux/objtool.h
> +++ b/include/linux/objtool.h
> @@ -90,6 +90,12 @@ struct unwind_hint {
> _ASM_PTR " 986b\n\t" \
> ".popsection\n\t"
>
> +#define ANNOTATE_NOSEAL \
> + "986: \n\t" \
> + ".pushsection .discard.noseal\n\t" \
> + _ASM_PTR " 986b\n\t" \
> + ".popsection\n\t"
> +
> #define ASM_REACHABLE \
> "998:\n\t" \
> ".pushsection .discard.reachable\n\t" \
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 0cec74da7ffe..0d04d0a707f4 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2111,6 +2111,40 @@ static int read_noendbr_hints(struct objtool_file *file)
> return 0;
> }
>
> +static void mark_endbr_used(struct instruction *insn)
> +{
> + if (!list_empty(&insn->call_node))
> + list_del_init(&insn->call_node);
> +}
> +
> +static int read_noseal_hints(struct objtool_file *file)
> +{
> + struct section *sec;
> + struct instruction *insn;
> + struct reloc *reloc;
> +
> + sec = find_section_by_name(file->elf, ".rela.discard.noseal");
> + if (!sec)
> + return 0;
> +
> + list_for_each_entry(reloc, &sec->reloc_list, list) {
> + insn = find_insn(file, reloc->sym->sec, reloc->sym->offset + reloc->addend);
> + if (!insn) {
> + WARN("bad .discard.noseal entry");
> + return -1;
> + }
> +
> + if (insn->type != INSN_ENDBR) {
> + WARN_FUNC("ANNOTATE_NOSEAL not on ENDBR", insn->sec, insn->offset);
> + continue;
> + }
> +
> + mark_endbr_used(insn);
> + }
> +
> + return 0;
> +}
> +
> static int read_retpoline_hints(struct objtool_file *file)
> {
> struct section *sec;
> @@ -2356,6 +2390,10 @@ static int decode_sections(struct objtool_file *file)
> if (ret)
> return ret;
>
> + ret = read_noseal_hints(file);
> + if (ret)
> + return ret;
> +
> /*
> * Must be before add_{jump_call}_destination.
> */
> @@ -3952,12 +3990,6 @@ static int validate_functions(struct objtool_file *file)
> return warnings;
> }
>
> -static void mark_endbr_used(struct instruction *insn)
> -{
> - if (!list_empty(&insn->call_node))
> - list_del_init(&insn->call_node);
> -}
> -
> static int validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
> {
> struct instruction *dest;
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