Re: [PATCH for-4.20 v5] Avoid crash calling PrintErrMesg from efi_multiboot2

[Oleksii Kurochko]

On 2/4/25 2:07 PM, Jan Beulich wrote:
On 22.01.2025 11:14, Frediano Ziglio wrote:
Although code is compiled with -fpic option data is not position
independent. This causes data pointer to become invalid if
code is not relocated properly which is what happens for
efi_multiboot2 which is called by multiboot entry code.
Code tested adding
    PrintErrMesg(L"Test message", EFI_BUFFER_TOO_SMALL);
in efi_multiboot2 before calling efi_arch_edd (this function
can potentially call PrintErrMesg).

Before the patch (XenServer installation on Qemu, xen replaced
with vanilla xen.gz):
   Booting `XenServer (Serial)'Booting `XenServer (Serial)'
   Test message: !!!! X64 Exception Type - 0E(#PF - Page-Fault)  CPU Apic ID - 
00000000 !!!!
   ExceptionData - 0000000000000000  I:0 R:0 U:0 W:0 P:0 PK:0 SS:0 SGX:0
   RIP  - 000000007EE21E9A, CS  - 0000000000000038, RFLAGS - 0000000000210246
   RAX  - 000000007FF0C1B5, RCX - 0000000000000050, RDX - 0000000000000010
   RBX  - 0000000000000000, RSP - 000000007FF0C180, RBP - 000000007FF0C210
   RSI  - FFFF82D040467CE8, RDI - 0000000000000000
   R8   - 000000007FF0C1C8, R9  - 000000007FF0C1C0, R10 - 0000000000000000
   R11  - 0000000000001020, R12 - FFFF82D040467CE8, R13 - 000000007FF0C1B8
   R14  - 000000007EA33328, R15 - 000000007EA332D8
   DS   - 0000000000000030, ES  - 0000000000000030, FS  - 0000000000000030
   GS   - 0000000000000030, SS  - 0000000000000030
   CR0  - 0000000080010033, CR2 - FFFF82D040467CE8, CR3 - 000000007FC01000
   CR4  - 0000000000000668, CR8 - 0000000000000000
   DR0  - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000
   DR3  - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400
   GDTR - 000000007F9DB000 0000000000000047, LDTR - 0000000000000000
   IDTR - 000000007F48E018 0000000000000FFF,   TR - 0000000000000000
   FXSAVE_STATE - 000000007FF0BDE0
   !!!! Find image based on IP(0x7EE21E9A) (No PDB)  
(ImageBase=000000007EE20000, EntryPoint=000000007EE23935) !!!!

After the patch:
   Booting `XenServer (Serial)'Booting `XenServer (Serial)'
   Test message: Buffer too small
   BdsDxe: loading Boot0000 "UiApp" from 
Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331)
   BdsDxe: starting Boot0000 "UiApp" from 
Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331)

This partially rollback commit 00d5d5ce23e6.

Fixes: 9180f5365524 ("x86: add multiboot2 protocol support for EFI platforms")
Signed-off-by: Frediano Ziglio<frediano.zig...@cloud.com>
I expect we want this in before the release. Oleksii? Maintainers?

Interesting it is a fix for a ~3 years old bug ( if to look at when9180f5365524 is introduced ) so it seems it happens not often. Anyway, I 
agree that we want this fix before the release: R-Acked-by: Oleksii 
Kurochko <oleksii.kuroc...@gmail.com> Thanks. ~ Oleksii


Jan