From: Borislav Petkov <bp@alien8.de>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Michael Roth <michael.roth@amd.com>
Subject: Re: [PATCH v2 02/16] x86/compressed: efi-mixed: move 32-bit entrypoint code into .text section
Date: Thu, 6 Oct 2022 13:13:44 +0200 [thread overview]
Message-ID: <Yz64aMVo4W+D70Fz@zn.tnic> (raw)
In-Reply-To: <CAMj1kXGCWmay_=cncZpZwXoyLgzt7=2dVuXHaaQU=K6NEXrezQ@mail.gmail.com>
On Thu, Oct 06, 2022 at 12:56:09PM +0200, Ard Biesheuvel wrote:
> efi32_pe_entry() preserves and restores the caller's value of %ebx,
> because from there, we might actually return control to the firmware.
> The value it keeps in %ebx itself is not live when it jumps to
> efi32_entry - it stores its value into image_offset, which is reloaded
> from memory at a later point.
Hmm, might be prudent to have a comment there because it is using %ebx a
couple of insns before the JMP:
subl %esi, %ebx
^^^^
movl %ebx, rva(image_offset)(%ebp) // save image_offset
<--- I think you mean that after this, %ebx is not needed anymore?
xorl %esi, %esi
jmp efi32_entry
2: popl %edi // restore callee-save registers
popl %ebx
and this restores its original value ofc.
> efi32_stub_entry() is the 'EFI handover protocol' entry point, which
> cannot return to the firmware (and we discard the return address
> already) so %ebx can be clobbered.
That info would be good to have in a comment above it.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-10-06 11:14 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 14:54 [PATCH v2 00/16] x86: head_64.S spring cleaning Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 01/16] x86/compressed: efi-mixed: rename efi_thunk_64.S to efi-mixed.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 02/16] x86/compressed: efi-mixed: move 32-bit entrypoint code into .text section Ard Biesheuvel
2022-10-06 10:42 ` Borislav Petkov
2022-10-06 10:56 ` Ard Biesheuvel
2022-10-06 11:13 ` Borislav Petkov [this message]
2022-10-06 11:19 ` Ard Biesheuvel
2022-10-06 12:27 ` Ard Biesheuvel
2022-10-07 8:56 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 03/16] x86/compressed: efi-mixed: move bootargs parsing out of 32-bit startup code Ard Biesheuvel
2022-10-06 11:03 ` Borislav Petkov
2022-10-06 11:29 ` Ard Biesheuvel
2022-10-07 9:30 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 04/16] x86/compressed: efi-mixed: move efi32_pe_entry into .text section Ard Biesheuvel
2022-11-17 15:57 ` Borislav Petkov
2022-11-17 16:06 ` Ard Biesheuvel
2022-11-17 17:08 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 05/16] x86/compressed: efi-mixed: move efi32_entry out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 06/16] x86/compressed: efi-mixed: move efi32_pe_entry() " Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 07/16] x86/compressed: efi: merge multiple definitions of image_offset into one Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 08/16] x86/compressed: efi-mixed: simplify IDT/GDT preserve/restore Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 09/16] x86/compressed: avoid touching ECX in startup32_set_idt_entry() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 10/16] x86/compressed: pull global variable ref up into startup32_load_idt() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 11/16] x86/compressed: move startup32_load_idt() into .text section Ard Biesheuvel
2022-11-18 16:44 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 12/16] x86/compressed: move startup32_load_idt() out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 13/16] x86/compressed: move startup32_check_sev_cbit() into .text Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 14/16] x86/compressed: move startup32_check_sev_cbit() out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 15/16] x86/compressed: adhere to calling convention in get_sev_encryption_bit() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 16/16] x86/compressed: only build mem_encrypt.S if AMD_MEM_ENCRYPT=y Ard Biesheuvel
2022-11-18 18:26 ` [PATCH v2 00/16] x86: head_64.S spring cleaning Borislav Petkov
2022-11-18 23:31 ` Ard Biesheuvel
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