x86/sev: Fix kernel crash due to late update to read-only ghcb_version
[ Upstream commit 27d25348d42161837be08fc63b04a2559d2e781c ]
A write-access violation page fault kernel crash was observed while running
cpuhotplug LTP testcases on SEV-ES enabled systems. The crash was
observed during hotplug, after the CPU was offlined and the process
was migrated to different CPU. setup_ghcb() is called again which
tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this
is a read_only variable which is initialised during booting.
Trying to write it results in a pagefault:
BUG: unable to handle page fault for address: ffffffffba556e70
#PF: supervisor write access in kernel mode
#PF: error_code(0x0003) - permissions violation
[ ...]
Call Trace:
<TASK>
? __die_body.cold+0x1a/0x1f
? __die+0x2a/0x35
? page_fault_oops+0x10c/0x270
? setup_ghcb+0x71/0x100
? __x86_return_thunk+0x5/0x6
? search_exception_tables+0x60/0x70
? __x86_return_thunk+0x5/0x6
? fixup_exception+0x27/0x320
? kernelmode_fixup_or_oops+0xa2/0x120
? __bad_area_nosemaphore+0x16a/0x1b0
? kernel_exc_vmm_communication+0x60/0xb0
? bad_area_nosemaphore+0x16/0x20
? do_kern_addr_fault+0x7a/0x90
? exc_page_fault+0xbd/0x160
? asm_exc_page_fault+0x27/0x30
? setup_ghcb+0x71/0x100
? setup_ghcb+0xe/0x100
cpu_init_exception_handling+0x1b9/0x1f0
The fix is to call sev_es_negotiate_protocol() only in the BSP boot phase,
and it only needs to be done once in any case.
[ mingo: Refined the changelog. ]
Fixes: 95d33bfaa3
("x86/sev: Register GHCB memory when SEV-SNP is active")
Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Co-developed-by: Bo Gan <bo.gan@broadcom.com>
Signed-off-by: Bo Gan <bo.gan@broadcom.com>
Signed-off-by: Ashwin Dayanand Kamat <ashwin.kamat@broadcom.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/1701254429-18250-1-git-send-email-kashwindayan@vmware.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
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@ -1234,10 +1234,6 @@ void setup_ghcb(void)
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if (!cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
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return;
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/* First make sure the hypervisor talks a supported protocol. */
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if (!sev_es_negotiate_protocol())
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sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
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/*
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* Check whether the runtime #VC exception handler is active. It uses
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* the per-CPU GHCB page which is set up by sev_es_init_vc_handling().
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@ -1254,6 +1250,13 @@ void setup_ghcb(void)
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return;
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}
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/*
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* Make sure the hypervisor talks a supported protocol.
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* This gets called only in the BSP boot phase.
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*/
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if (!sev_es_negotiate_protocol())
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sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
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/*
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* Clear the boot_ghcb. The first exception comes in before the bss
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* section is cleared.
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