From nobody Fri Nov 29 02:37:56 2024 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5AD5218C920 for ; Wed, 25 Sep 2024 15:02:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727276541; cv=none; b=lVhegDNQuZHlE/okac15dNy8541Bw6cTaVqG2qAO8KEMHqdnP+tQMcyBa9Gb7vM73kt+0xO/I41mLcxoetCRMAFScf5Y8EbrauTztd60mCpAaS/tmQUEqKTxDn/JFILKQ04MOPXnbIPPaixqhVqse8f1cGoidjUN6tuvO0j14n8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727276541; c=relaxed/simple; bh=JTcZMRf52oQJjvsrQbaaa26wNEschMPTichZxc3ZyTY=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=RveKIH22mLgZJUXx71FosIo9pmXrEgbR1F+sZ/IPwxYMP3ZnJY0H+ng+FiyEWLUMF/r9SMJTXekQJUhuxBrK8gckANCgCAp1Jgt+1CI6dxQH5fG/1HQF+tOzy35wE5+HJrGQ2krB8bzlAfnwtKmKxNJpjeEE0B3OszbCJVqTlwY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--ardb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=CjZEe0yN; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--ardb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="CjZEe0yN" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-6ddbcc96a5fso96281457b3.0 for ; Wed, 25 Sep 2024 08:02:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1727276538; x=1727881338; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=WebA59vxPkU4u7rhQajyH4BvEeqGZRhskbQXw1lowfs=; b=CjZEe0yNT4EA/GcKFh/6Jssm8m05B25tkcW0KFhhtewe6SRdV2pEBLGa8yx/CpnYXJ MfntbYWoR1EhxjADX4+aOngkHAyjORnocT0BwOjgiFWm6L9HcXyB25UtRC5WVEKXYQ8/ OBJp+RzevUhpU5cFWOu9jzr/vhzsqrDj6GDAUkaYRak0E/z6D3Yf/fm8f5JZrtMWcMnl N2qyh7vfxeYL30RgFZtnhXpuFyZSZTj5isYZ0+Nn1pn+I+DNbcSSB5DAZw7YyVlBXAoM 1qDDv2bg/JAR0EqiibTG7Li9wPtqRa1ga4t+tABXo/xjQIYYy2wNNwNCHH8jY+xfdOcT OWug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727276538; x=1727881338; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=WebA59vxPkU4u7rhQajyH4BvEeqGZRhskbQXw1lowfs=; b=A5r9YSgjoKcshPGExRYJBPwhii9a2doC84NKBpEyL3o2hGdJcSNc9+5rfQSavU3lef McASlquWJyD57YnUMvzbmcm0IaLyJHwPtrRPR2cfg8jGPAjH1wIlyJErhxFppUf0m+BG IQwXHdorCPaT9ik+9F2vEyTChAnzi6FhpxPDstjv2/ovJdijFm6Ih3FlwMXstr8bM0Qp Y3FenMfzqkk/GJX2rO4FSAXmg60i2tnG2zYpmDKiMabtSUkgDFEcXs/GZ0opXOt7U/Ph 0D68wXSfMwuBig67F1xBP0nYnAb1/rj/7i2HL+5WEKfrgzwlgY37U3t9pcTDqFDRuNOn 99zA== X-Gm-Message-State: AOJu0YwSao45TXPmrPki4l00OlsmKVMxJDm15xFJ1WjHV0ueepeY5Xqz 1ebYaf7PA9rFkWtvqmMzZsZG3ItmdY2xDQq9BxS6uWI9yqdtJLKpVgOvCcoO/JIGrfcP3Q4+fp7 mLpte+C1IvEczjPQ6nDYmcDNZpZDjPDXWlkddHZsidh9r2wW/R5LV900M4x4EsEzrJ746Q8dXu/ zRPrB6PKjGqf6h0csmXD5T3jAoHQzybQ== X-Google-Smtp-Source: AGHT+IG1eaRHJ+k+oWi0MEewfWnHRvzWiyuPrZa2XUixnuMGDlz9gyzzCn4pjg7USYksDYWFG76nQbXB X-Received: from palermo.c.googlers.com ([fda3:e722:ac3:cc00:7b:198d:ac11:8138]) (user=ardb job=sendgmr) by 2002:a81:7c46:0:b0:673:b39a:92ce with SMTP id 00721157ae682-6e21da5ea7bmr151347b3.3.1727276537527; Wed, 25 Sep 2024 08:02:17 -0700 (PDT) Date: Wed, 25 Sep 2024 17:01:11 +0200 In-Reply-To: <20240925150059.3955569-30-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240925150059.3955569-30-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=3674; i=ardb@kernel.org; h=from:subject; bh=R6ohiPGa3ul2ikQd2A7YE6wpEPvXq0bd6W2LGMrzZ/k=; b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe2L6m4L/Wkc7n0aPQzsYULiEQZPMlgefsmsLHv4K8KPe c6T1d0dpSwMYhwMsmKKLAKz/77beXqiVK3zLFmYOaxMIEMYuDgFYCLF8YwMhwNCO7WWnu4+bHJ/ R+KN+e/7+Z5GTZy4J83mRy0Xx+UbAowMLwuTAsXUc+SfqAVdK+gtnHdHT+jRjZtrv3D/ms77oD2 BCwA= X-Mailer: git-send-email 2.46.0.792.g87dc391469-goog Message-ID: <20240925150059.3955569-41-ardb+git@google.com> Subject: [RFC PATCH 11/28] x86/pvh: Avoid absolute symbol references in .head.text From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: Ard Biesheuvel , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Uros Bizjak , Dennis Zhou , Tejun Heo , Christoph Lameter , Mathieu Desnoyers , Paolo Bonzini , Vitaly Kuznetsov , Juergen Gross , Boris Ostrovsky , Greg Kroah-Hartman , Arnd Bergmann , Masahiro Yamada , Kees Cook , Nathan Chancellor , Keith Packard , Justin Stitt , Josh Poimboeuf , Arnaldo Carvalho de Melo , Namhyung Kim , Jiri Olsa , Ian Rogers , Adrian Hunter , Kan Liang , linux-doc@vger.kernel.org, linux-pm@vger.kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, linux-efi@vger.kernel.org, linux-arch@vger.kernel.org, linux-sparse@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-perf-users@vger.kernel.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel The .head.text section contains code that may execute from a different address than it was linked at. This is fragile, given that the x86 ABI can refer to global symbols via absolute or relative references, and the toolchain assumes that these are interchangeable, which they are not in this particular case. In the case of the PVH code, there are some additional complications: - the absolute references are in 32-bit code, which get emitted with R_X86_64_32 relocations, and these are not permitted in PIE code; - the code in question is not actually relocatable: it can only run correctly from the physical load address specified in the ELF note. So rewrite the code to only rely on relative symbol references: these are always 32-bits wide, even in 64-bit code, and are resolved by the linker at build time. Signed-off-by: Ard Biesheuvel --- arch/x86/platform/pvh/head.S | 39 ++++++++++++++------ 1 file changed, 27 insertions(+), 12 deletions(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index adbf57e83e4e..e6cb7da40e09 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -54,7 +54,20 @@ SYM_CODE_START(pvh_start_xen) UNWIND_HINT_END_OF_STACK cld =20 - lgdt (_pa(gdt)) + /* + * This is position dependent code that can only execute correctly from + * the physical address that the kernel was linked to run at. Use the + * symbols emitted for the ELF note to construct the build time physical + * address of pvh_start_xen(), without relying on absolute 32-bit ELF + * relocations, as these are not supported by the linker when running in + * -pie mode, and should be avoided in .head.text in general. + */ +0: mov $xen_elfnote_phys32_entry_offset - 0b, %ebp + sub $xen_elfnote_phys32_entry - 0b, %ebp + + lea (gdt - pvh_start_xen)(%ebp), %eax + add %eax, 2(%eax) + lgdt (%eax) =20 mov $PVH_DS_SEL,%eax mov %eax,%ds @@ -62,14 +75,14 @@ SYM_CODE_START(pvh_start_xen) mov %eax,%ss =20 /* Stash hvm_start_info. */ - mov $_pa(pvh_start_info), %edi + lea (pvh_start_info - pvh_start_xen)(%ebp), %edi mov %ebx, %esi - mov _pa(pvh_start_info_sz), %ecx + mov (pvh_start_info_sz - pvh_start_xen)(%ebp), %ecx shr $2,%ecx rep movsl =20 - mov $_pa(early_stack_end), %esp + lea (early_stack_end - pvh_start_xen)(%ebp), %esp =20 /* Enable PAE mode. */ mov %cr4, %eax @@ -84,17 +97,21 @@ SYM_CODE_START(pvh_start_xen) wrmsr =20 /* Enable pre-constructed page tables. */ - mov $_pa(init_top_pgt), %eax + lea (init_top_pgt - pvh_start_xen)(%ebp), %eax mov %eax, %cr3 mov $(X86_CR0_PG | X86_CR0_PE), %eax mov %eax, %cr0 =20 /* Jump to 64-bit mode. */ - ljmp $PVH_CS_SEL, $_pa(1f) + lea (1f - pvh_start_xen)(%ebp), %eax + push $PVH_CS_SEL + push %eax + lret =20 /* 64-bit entry point. */ .code64 1: + UNWIND_HINT_END_OF_STACK /* Clear %gs so early per-CPU references target the per-CPU load area */ mov $MSR_GS_BASE,%ecx xor %eax, %eax @@ -108,10 +125,8 @@ SYM_CODE_START(pvh_start_xen) call *%rax =20 /* startup_64 expects boot_params in %rsi. */ - mov $_pa(pvh_bootparams), %rsi - mov $_pa(startup_64), %rax - ANNOTATE_RETPOLINE_SAFE - jmp *%rax + lea pvh_bootparams(%rip), %rsi + jmp startup_64 =20 #else /* CONFIG_X86_64 */ =20 @@ -146,8 +161,8 @@ SYM_CODE_END(pvh_start_xen) .section ".init.data","aw" .balign 8 SYM_DATA_START_LOCAL(gdt) - .word gdt_end - gdt_start - .long _pa(gdt_start) + .word gdt_end - gdt_start - 1 + .long gdt_start - gdt .word 0 SYM_DATA_END(gdt) SYM_DATA_START_LOCAL(gdt_start) --=20 2.46.0.792.g87dc391469-goog