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Fri, 18 Nov 2022 20:10:39 -0500 (EST) Date: Fri, 18 Nov 2022 20:10:33 -0500 From: Demi Marie Obenour To: Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= Cc: Ard Biesheuvel , linux-efi@vger.kernel.org, Xen developer discussion , Peter Jones , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Kees Cook , Anton Vorontsov , Colin Cross , Tony Luck Subject: Re: [PATCH v2 5/6] efi: xen: Implement memory descriptor lookup based on hypercall Message-ID: References: <20221003112625.972646-1-ardb@kernel.org> <20221003112625.972646-6-ardb@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="eZXLIpVKxA42QWNq" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org --eZXLIpVKxA42QWNq Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Date: Fri, 18 Nov 2022 20:10:33 -0500 From: Demi Marie Obenour To: Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= Cc: Ard Biesheuvel , linux-efi@vger.kernel.org, Xen developer discussion , Peter Jones , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Kees Cook , Anton Vorontsov , Colin Cross , Tony Luck Subject: Re: [PATCH v2 5/6] efi: xen: Implement memory descriptor lookup based on hypercall On Mon, Oct 03, 2022 at 07:04:02PM +0200, Marek Marczykowski-G=C3=B3recki w= rote: > On Mon, Oct 03, 2022 at 06:37:19PM +0200, Ard Biesheuvel wrote: > > On Mon, 3 Oct 2022 at 18:23, Demi Marie Obenour > > wrote: > > > > > > On Mon, Oct 03, 2022 at 05:59:52PM +0200, Ard Biesheuvel wrote: > > > > On Mon, 3 Oct 2022 at 17:29, Demi Marie Obenour > > > > wrote: > > > > > > > > > > On Mon, Oct 03, 2022 at 01:26:24PM +0200, Ard Biesheuvel wrote: > > > > > > Xen on x86 boots dom0 in EFI mode but without providing a memor= y map. > > > > > > This means that some sanity checks we would like to perform on > > > > > > configuration tables or other data structures in memory are not > > > > > > currently possible. Xen does, however, expose EFI memory descri= ptor info > > > > > > via a Xen hypercall, so let's wire that up instead. > > > > > > > > > > > > Co-developed-by: Demi Marie Obenour > > > > > > Signed-off-by: Demi Marie Obenour > > > > > > Signed-off-by: Ard Biesheuvel > > > > > > --- > > > > > > drivers/firmware/efi/efi.c | 5 ++- > > > > > > drivers/xen/efi.c | 34 ++++++++++++++++++++ > > > > > > include/linux/efi.h | 1 + > > > > > > 3 files changed, 39 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/= efi.c > > > > > > index 55bd3f4aab28..2c12b1a06481 100644 > > > > > > --- a/drivers/firmware/efi/efi.c > > > > > > +++ b/drivers/firmware/efi/efi.c > > > > > > @@ -456,7 +456,7 @@ void __init efi_find_mirror(void) > > > > > > * and if so, populate the supplied memory descriptor with the= appropriate > > > > > > * data. > > > > > > */ > > > > > > -int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_= md) > > > > > > +int __efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *ou= t_md) > > > > > > { > > > > > > efi_memory_desc_t *md; > > > > > > > > > > > > @@ -485,6 +485,9 @@ int efi_mem_desc_lookup(u64 phys_addr, efi_= memory_desc_t *out_md) > > > > > > return -ENOENT; > > > > > > } > > > > > > > > > > > > +extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_= t *out_md) > > > > > > + __weak __alias(__efi_mem_desc_lookup); > > > > > > + > > > > > > /* > > > > > > * Calculate the highest address of an efi memory descriptor. > > > > > > */ > > > > > > diff --git a/drivers/xen/efi.c b/drivers/xen/efi.c > > > > > > index d1ff2186ebb4..74f3f6d8cdc8 100644 > > > > > > --- a/drivers/xen/efi.c > > > > > > +++ b/drivers/xen/efi.c > > > > > > @@ -26,6 +26,7 @@ > > > > > > > > > > > > #include > > > > > > #include > > > > > > +#include > > > > > > #include > > > > > > #include > > > > > > > > > > > > @@ -292,3 +293,36 @@ void __init xen_efi_runtime_setup(void) > > > > > > efi.get_next_high_mono_count =3D xen_efi_get_next_high= _mono_count; > > > > > > efi.reset_system =3D xen_efi_reset_system; > > > > > > } > > > > > > + > > > > > > +int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_= md) > > > > > > +{ > > > > > > + static_assert(XEN_PAGE_SHIFT =3D=3D EFI_PAGE_SHIFT, > > > > > > + "Mismatch between EFI_PAGE_SHIFT and XEN_PA= GE_SHIFT"); > > > > > > + struct xen_platform_op op =3D { > > > > > > + .cmd =3D XENPF_firmware_info, > > > > > > + .u.firmware_info =3D { > > > > > > + .type =3D XEN_FW_EFI_INFO, > > > > > > + .index =3D XEN_FW_EFI_MEM_INFO, > > > > > > + .u.efi_info.mem.addr =3D phys_addr, > > > > > > + .u.efi_info.mem.size =3D U64_MAX - phys_a= ddr, > > > > > > + } > > > > > > + }; > > > > > > + union xenpf_efi_info *info =3D &op.u.firmware_info.u.efi_= info; > > > > > > + int rc; > > > > > > + > > > > > > + if (!efi_enabled(EFI_PARAVIRT) || efi_enabled(EFI_MEMMAP)) > > > > > > + return __efi_mem_desc_lookup(phys_addr, out_md); > > > > > > + > > > > > > + rc =3D HYPERVISOR_platform_op(&op); > > > > > > + if (rc) { > > > > > > + pr_warn("Failed to lookup header 0x%llx in Xen me= mory map: error %d\n", > > > > > > + phys_addr, rc); > > > > > > + } > > > > > > + > > > > > > + out_md->phys_addr =3D info->mem.addr; > > > > > > > > > > This will be equal to phys_addr, not the actual start of the memo= ry > > > > > region. > > > > > > > > > > > + out_md->num_pages =3D info->mem.size >> EFI_PAGE_SH= IFT; > > > > > > > > > > Similarly, this will be the number of bytes in the memory region > > > > > after phys_addr, not the total number of bytes in the region. Th= ese two > > > > > differences mean that this function is not strictly equivalent to= the > > > > > original efi_mem_desc_lookup(). > > > > > > > > > > I am not sure if this matters in practice, but I thought you woul= d want > > > > > to be aware of it. > > > > > > > > This is a bit disappointing. Is there no way to obtain this > > > > information via a Xen hypercall? > > > > > > It is possible, but doing so is very complex (it essentially requires= a > > > binary search). This really should be fixed on the Xen side. > > > > > > > In any case, it means we'll need to round down phys_addr to page si= ze > > > > at the very least. > > > > > > That makes sense. Are there any callers that will be broken even with > > > this rounding? > >=20 > > As far as I can tell, it should work fine. The only thing to double > > check is whether we are not creating spurious error messages from > > efi_arch_mem_reserve() this way, but as far as I can tell, that should > > be fine too. > >=20 > > Is there anyone at your end that can give this a spin on an actual > > Xen/x86 system? >=20 > Demi, if you open a PR with this at > https://github.com/QubesOS/qubes-linux-kernel/pulls, I can run it > through our CI - (at least) one of the machines has ESRT table. Done: https://github.com/QubesOS/qubes-linux-kernel/pull/681 > AFAIR your test laptop has it too. It does; I plan to test a version that has the needed rounding. --=20 Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab --eZXLIpVKxA42QWNq Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEdodNnxM2uiJZBxxxsoi1X/+cIsEFAmN4LQ4ACgkQsoi1X/+c IsHajw//UHBxXvpBAaynVshK24kWcagS+15BbXEqlSvj8f4y7Kjd/j71nedJG9wM fbDlTd9ThZh+Bts17ytNdVxxx1NPN0vwm9Y65alkMraBBS0zKlbSMLofYTBHc4K5 k9JxkuEejvWOYXKEHzDXIong/pKBMa1LFQVrkS/SfV8KpRm8jAS7+a/+5MnzsRP5 iAQ89uiCJO2fipRHlw7dEnwMy1UR7S/huHUaKh0Zjdyu3LGFNVkPC1LE43BVg8rB 2nwkfGpBcnHvGmG74/DC3SoPdlA89NCSaJnbJzY+0eEfkhZrZBaV4C7+MLCljXeQ mDGyTDLYWpt5GKv52OfL1UmW1qlp2b1cn8mADcqAHFGKyWzhvsfV16J+q1p9eJ4f xeX7PIYpHefhifjHnghR792HoVYaHrzz0fELsYlBCYxkysSzACpUbdgOXI3CJZ2u nTuI+ktChEb9+EoV5ZF3RWzWjIQRLRZBkAXZdLuFn0+VKojnirSTf5UeBsqORStK sNuHUirH2Y917nSidGZjAcMeh7wg1gA6nTx/zvfR+hoGZW7BUdlqbWUKHFyu8PqN vlosBmJp16MCylNe61+1fxyM78dfpTMd72jHwJLyq71Na+WgiRXuCFUoADHCi6He 0KH4QOPfjJ0xYOokeSnC/6MNGIBYJdUaxxKUGgdQKSZ5emLd5WI= =ahFb -----END PGP SIGNATURE----- --eZXLIpVKxA42QWNq--