Re: [PATCH v7 6/6] KVM: arm64: Symbolize the nVHE HYP addresses

From: Marc Zyngier <maz@kernel.org>
To: Kalesh Singh <kaleshsingh@google.com>
Cc: will@kernel.org, qperret@google.com, tabba@google.com,
	surenb@google.com, kernel-team@android.com,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Andrew Walbran <qwandor@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Andrew Jones <drjones@redhat.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Changbin Du <changbin.du@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 6/6] KVM: arm64: Symbolize the nVHE HYP addresses
Date: Mon, 18 Apr 2022 11:16:50 +0100	[thread overview]
Message-ID: <87tuaqae7h.wl-maz@kernel.org> (raw)
In-Reply-To: <20220408200349.1529080-7-kaleshsingh@google.com>

On Fri, 08 Apr 2022 21:03:29 +0100,
Kalesh Singh <kaleshsingh@google.com> wrote:
> 
> Reintroduce the __kvm_nvhe_ symbols in kallsyms, ignoring the local
> symbols in this namespace. The local symbols are not informative and
> can cause aliasing issues when symbolizing the addresses.
> 
> With the necessary symbols now in kallsyms we can symbolize nVHE
> addresses using the %p print format specifier:
> 
> [   98.916444][  T426] kvm [426]: nVHE hyp panic at: [<ffffffc0096156fc>] __kvm_nvhe_overflow_stack+0x8/0x34!
> 
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> ---
> 
> Changes in v6:
>   - Add Fuad's Reviewed-by and Tested-by tags.
>   
> Changes in v2:
>   - Fix printk warnings - %p expects (void *)
> 
> 
>  arch/arm64/kvm/handle_exit.c | 13 +++++--------
>  scripts/kallsyms.c           |  2 +-
>  2 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 97fe14aab1a3..a377b871bf58 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -295,13 +295,8 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
>  	u64 elr_in_kimg = __phys_to_kimg(elr_phys);
>  	u64 hyp_offset = elr_in_kimg - kaslr_offset() - elr_virt;
>  	u64 mode = spsr & PSR_MODE_MASK;
> +	u64 panic_addr = elr_virt + hyp_offset;
>  
> -	/*
> -	 * The nVHE hyp symbols are not included by kallsyms to avoid issues
> -	 * with aliasing. That means that the symbols cannot be printed with the
> -	 * "%pS" format specifier, so fall back to the vmlinux address if
> -	 * there's no better option.
> -	 */
>  	if (mode != PSR_MODE_EL2t && mode != PSR_MODE_EL2h) {
>  		kvm_err("Invalid host exception to nVHE hyp!\n");
>  	} else if (ESR_ELx_EC(esr) == ESR_ELx_EC_BRK64 &&
> @@ -321,9 +316,11 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
>  		if (file)
>  			kvm_err("nVHE hyp BUG at: %s:%u!\n", file, line);
>  		else
> -			kvm_err("nVHE hyp BUG at: %016llx!\n", elr_virt + hyp_offset);
> +			kvm_err("nVHE hyp BUG at: [<%016llx>] %pB!\n", panic_addr,
> +					(void *)panic_addr);
>  	} else {
> -		kvm_err("nVHE hyp panic at: %016llx!\n", elr_virt + hyp_offset);
> +		kvm_err("nVHE hyp panic at: [<%016llx>] %pB!\n", panic_addr,
> +				(void *)panic_addr);
>  	}
>  
>  	/*
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 8caabddf817c..ad2c93640a92 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -111,7 +111,7 @@ static bool is_ignored_symbol(const char *name, char type)
>  		".L",			/* local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */
>  		"__crc_",		/* modversions */
>  		"__efistub_",		/* arm64 EFI stub namespace */
> -		"__kvm_nvhe_",		/* arm64 non-VHE KVM namespace */
> +		"__kvm_nvhe_$",		/* arm64 local symbols in non-VHE KVM namespace */
>  		"__AArch64ADRPThunk_",	/* arm64 lld */
>  		"__ARMV5PILongThunk_",	/* arm lld */
>  		"__ARMV7PILongThunk_",

If you are sanitising this, shouldn'tt you also apply the same rules
as the rest of the kernel for non-'__-kvm_nvhe_' symbols? For example,
I see a long list of .L* symbols:

0000000000000000 r __kvm_nvhe_.L144721
0000000000000090 r __kvm_nvhe_.L144721
00000000000000b4 r __kvm_nvhe_.L144721
00000000000004b0 r __kvm_nvhe_.L144721
000000000000051c r __kvm_nvhe_.L144721
0000000000000650 r __kvm_nvhe_.L144721
0000000000000694 r __kvm_nvhe_.L144721
0000000000000761 r __kvm_nvhe_.L144721
00000000000007a7 r __kvm_nvhe_.L144721
00000000000007c7 r __kvm_nvhe_.L144721
0000000000000814 r __kvm_nvhe_.L144721
0000000000000b08 r __kvm_nvhe_.L144721
0000000000003200 r __kvm_nvhe_.L144721

(83 of them in total on a local build) that I think should also be
trimmed.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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