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Mon, 23 Sep 2024 08:17:24 -0700 (PDT) Message-ID: <47fc5e0d-e249-4e69-b19d-bb2c4edd1abd@suse.com> Date: Mon, 23 Sep 2024 17:17:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] x86: Put trampoline in separate .init.trampoline section To: Frediano Ziglio Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , xen-devel@lists.xenproject.org References: <20240919080021.20155-1-frediano.ziglio@cloud.com> <20240919080021.20155-2-frediano.ziglio@cloud.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <20240919080021.20155-2-frediano.ziglio@cloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 19.09.2024 10:00, Frediano Ziglio wrote: > This change put the trampoline in a separate, not executable section. > The trampoline contains a mix of code and data (data which > is modified from C code during early start so must be writable). > This is in preparation for W^X patch in order to satisfy UEFI CA > memory mitigation requirements. > At the moment .init.text and .init.data in EFI mode are put together > so they will be in the same final section as before this patch. > Putting in a separate section (even in final executables) allows > to easily disassembly that section. As we need to have a writable > section and as we can't have code and data together to satisfy W^X > requirement we need to have a data section. However tools like objdump > by default do not disassemble data sections. Forcing disassembly of > data sections would result in a very large output and possibly crash > of tools. Putting in a separate section allows to selectively > disassemble that part of code using a command like > > objdump -m i386 -j .init.trampoline -d xen-syms For xen.efi it won't be quite as neat. One of the reason all .init.* are folded into a single section there is that the longer section names aren't properly represented, because of the linker apparently preferring to truncate them instead of using the "long section names" extension. To disassemble there one will need to remember to use "-j .init.tr". I'll have to check if there's a linker option we fail to enable, but in the absence of that we may want to consider to name the output section just ".trampoline" there, abbreviating to ".trampol" (i.e. at least a little more descriptive). > --- a/xen/arch/x86/boot/head.S > +++ b/xen/arch/x86/boot/head.S > @@ -882,8 +882,9 @@ cmdline_parse_early: > reloc: > .incbin "reloc.bin" > > +#include "x86_64.S" > + > + .section .init.trampoline, "aw", @progbits I think the lack of x here requires a comment. Also did I miss any reply by you to Andrew's suggestion to move the trampoline to its own translation unit? Jan